Correction of the workaround: instead of                                                            

echo 'RPM::Allow-Duplicated { "libgmp"; };' > /etc/apt/apt.conf.d/libgmp-compat.conf

it's better to put a more precise pattern there:                                  

echo 'RPM::Allow-Duplicated { "^libgmp$"; };' > /etc/apt/apt.conf.d/libgmp-compat.conf

Illustration -- the removal of old libgmp causes an upgrade of a lot of packages from p6, so it's desirable to be able to keep it:

apt> remove libgmp#4.3.2-alt3 
Чтобы выполнить эту операцию необходимы изменения, которые не были запрошены.
Следующие пакеты будут ОБНОВЛЕНЫ:
  GConf ModemManager NetworkManager NetworkManager-glib NetworkManager-l2tp NetworkManager-openvpn NetworkManager-pptp NetworkManager-vpnc alacarte audit bacula-client bacula-common bacula-console
  bacula-director-common bacula-director-sqlite3 bacula-storage compiz dconf dhcpcd dnsmasq dropbox eiskaltdcpp-common eiskaltdcpp-gtk-data etcnet etcnet-defaults-desktop glib2 glib2-locales glxinfo
  gnome-search-tool gobject-introspection gphoto2 gpsd gsettings-desktop-schemas gst-plugins-nice hplip-PPDs hplip-common hplip-hpcups hplip-hpcups-PPDs hplip-hpijs hplip-hpijs-PPDs hplip-ps-PPDs iotop
  kde-common kde4base-runtime-common libGConf libGL libGLU libX11 libX11-locales libalsa libapr1 libaprutil1 libatk libatk-gir libatk-locales libaudit1 libauparse0 libdconf libeiskaltdcpp libexiv2 libexpat
  libfltk13 libfreerdp libgdk-pixbuf libgdk-pixbuf-gir libgdk-pixbuf-locales libgeoclue libgexiv2 libgio libglibmm libglpk libgnome-bluetooth libgnome-keyring libgnome-menus libgphoto2 libgps libgssdp
  libgtkpod libgupnp libgupnp-igd libgweather libgweather-data liblcms2 libmetis libmono libmusicbrainz3 libnautilus libnice libnumpy libpciaccess libpcre3 libpixman libpng12 libpodofo libpulseaudio libpurple
  libselinux libselinux-utils libstartup-notification libsubversion libsuitesparse libsynfig libsynfigstudio libtelepathy-glib libv8 libvte libxcb libxcbutil lshw maxima-bin-sbcl maxima-common mono
  mono-mscorlib nautilus-sendto nss_ldap openresolv openresolv-dnsmasq perl-Compress-Raw-Bzip2 perl-Compress-Raw-Zlib perl-DBI perl-DBM perl-Digest-SHA1 perl-Encode perl-HTML-Parser perl-Locale-gettext
  perl-Math-BigInt perl-Math-BigInt-FastCalc perl-Mozilla-LDAP perl-Net-SSLeay perl-Socket6 perl-Term-ReadKey perl-Term-ReadLine-Gnu perl-XML-LibXML perl-XML-Parser perl-base perl-devel perl-threads
  perl-unicore printer-drivers-base pulseaudio-utils python python-base python-dev python-module-BeautifulSoup python-module-OpenSSL python-module-Pygments python-module-Reportlab python-module-beaker
  python-module-compizconfig python-module-configobj python-module-cssutils python-module-gnome-menus python-module-imaging python-module-jinja2 python-module-jinja2-tests python-module-libasyncns
  python-module-mpmath python-module-nose python-module-numpy python-module-numpy-addons python-module-numpy-testing python-module-protobuf python-module-pygnome-desktop python-module-pyorbit
  python-module-pyxdg python-module-rope python-module-simplejson python-module-sip python-module-tempita python-modules python-modules-bsddb python-modules-compiler python-modules-ctypes
  python-modules-curses python-modules-email python-modules-encodings python-modules-hotshot python-modules-json python-modules-logging python-modules-multiprocessing python-modules-sqlite3
  python-modules-tkinter python-modules-wsgiref python-modules-xml python-strict remmina remmina-plugins sbcl service smem subversion subversion-perl transmission-common transmission-gui-common uniconvertor
  vala xorg-dri-swrast
Следующие пакеты будут ЗАМЕНЕНЫ:
  gnome-menus-common (by libgnome-menus)
Следующие пакеты будут УДАЛЕНЫ:
  389-admin 389-admin-console 389-admin-console-doc 389-ds 389-ds-devel 7colors NetworkManager-gnome NetworkManager-l2tp-gnome NetworkManager-openvpn-gnome NetworkManager-pptp-gnome NetworkManager-vpnc-gnome
  R-base R-doc-html R-tcltk Terminal Thunar TiMidity++ alsa-plugins-pulse alsa-tools alterator-auth alterator-net-shares alterator-x11 alterator-xkb anjuta2 apt-indicator audacity avahi-ui banshee
  banshee-ipod blueman branding-simply-linux-xfce-settings brasero calibre ccsm cheese chestnut-dialer chestnut-dialer-gtk2 chromium compiz-gtk easytag eiskaltdcpp-gtk emacs-maxima empathy epiphany
  epiphany-extensions evince evolution-data-server exfalso farsight2 firefox firefox-ru fslint fslint-gnome fusion-icon gajim gcalctool gdm-theme-simply gdm2.20 gecko-mediaplayer gedit gedit-plugins ghc-alex
  ghc-c2hs ghc-happy ghc-threadscope gimp gimp-plugin-exif-browser gimp-plugin-gutenprint gnome-alsamixer gnome-games-gir gnome-games-glchess gnome-games-glines gnome-games-gnect gnome-games-gnobots
  gnome-games-gnomine gnome-games-gnotravex gnome-games-gnotski gnome-games-gtali gnome-games-iagno gnome-games-sol gnome-games-sudoku gnome-libs gnome-media-common gnome-mplayer gnome-system-monitor
  gnome-vfs gst-plugins-base gst-plugins-good gthumb gtk2-theme-clearlooks gtk2-theme-simplicity gtk2-themes-xfce4 gtklp gtkpod gucharmap homebank hplip hplip-gui hplip-sane inkscape ipython kde4-kmid
  kde4base-runtime kde4base-runtime-core kde4base-workspace-core kde4edu-cantor koffice-core koffice-kword ldap-user-tools libavahi-gobject libavahi-ui-gtk3 libbonoboui libbrasero libcanberra libcanberra-gtk2
  libchamplain libchamplain-gtk libcheese libclutter-gir libclutter-gtk libevince libgdl libgkeyfile-sharp libgksu libglademm libgladeui libgluezilla libgmp#4.3.2-alt3 libgmp-devel#4.3.2-alt3 libgnome
  libgnome-panel libgnome-sharp libgnomeui libgoocanvas libgoogle-data-mono libgpod-sharp libgtk-sharp2 libgtkmm2 libgtksourceview libgudev-sharp libkeybinder libkwalletbackend4 libmetacity libmolletnetwork4
  libnepomukdatamanagement4 libnepomuksync4 libnet-snmp26 libnotify-sharp libreoffice libreoffice-gnome libreoffice-langpack-ru libsexy libtelepathy-farsight libtracker-client libunicapgtk libwebkitgtk2
  libxfce4ui libxfcegui4 libxfsm lshw-gui medit mintmenu mono-addins mono-data mono-data-sqlite mono-extras mono-wcf mono-web mono-winforms mozilla-plugin-adobe-flash mozilla-plugin-java-1.7.0-openjdk
  mozilla-plugin-vlc mplayer octave openldap2.4-servers pavucontrol perl4-compat pidgin pidgin-libnotify pitivi pulseaudio-daemon python-module-ClientForm python-module-Crypto python-module-OpenGL
  python-module-PyQt4 python-module-apt python-module-argparse python-module-avahi python-module-babel python-module-cups python-module-cupshelpers python-module-dateutil python-module-dbus
  python-module-docutils python-module-fusion-icon-gtk python-module-genshi python-module-gst python-module-html5lib python-module-kde4 python-module-libxml2 python-module-lxml python-module-mako
  python-module-matplotlib python-module-matplotlib-gtk python-module-mechanize python-module-mutagen python-module-notify python-module-numdifftools python-module-paramiko python-module-pexpect
  python-module-pyExcelerator python-module-pyalsa python-module-pycairo python-module-pygi python-module-pygnome python-module-pygnome-applet python-module-pygnome-bonobo python-module-pygnome-canvas
  python-module-pygnome-deskbar-applet python-module-pygnome-extras python-module-pygnome-gconf python-module-pygnome-gnome-vfs python-module-pygobject python-module-pygoocanvas python-module-pygtk
  python-module-pygtk-libglade python-module-pygtk_git python-module-pygtksourceview python-module-pylib python-module-pytz python-module-scikits python-module-scikits.statsmodels python-module-scipy
  python-module-serial python-module-setuptools python-module-sexy python-module-smbc python-module-sphinx python-module-sympy python-module-sympy-examples python-module-sympy-tests python-module-twisted-core
  python-module-vte python-module-webob python-module-xlwt python-module-zope python-module-zope.interface quodlibet samba-winbind seamonkey shotwell simple-ccsm sound-juicer stardict-gtk stardict-mueller7
  stardict-slovnyk_en-uk stardict-slovnyk_ru-en stardict-slovnyk_uk-en stardict-slovnyk_uk-ru sympy synaptic synaptic-usermode synfigstudio system-config-printer system-config-printer-udev telepathy-gabble
  telepathy-salut thunar-archive-plugin thunar-dropbox-plugin thunar-media-tags-plugin thunar-plugger thunar-plugger-dropbox thunar-shares-plugin thunar-volman-plugin thunderbird tracker transmission-gtk
  ucview uvcview wm-select xfcalendar xfce-utils xfce4-appfinder xfce4-battery-plugin xfce4-clipman-plugin xfce4-cpufreq-plugin xfce4-cpugraph-plugin xfce4-datetime-plugin xfce4-default xfce4-diskperf-plugin
  xfce4-eyes-plugin xfce4-fsguard-plugin xfce4-icon-theme xfce4-mailwatch-plugin xfce4-minimal xfce4-mixer xfce4-mount-plugin xfce4-netload-plugin xfce4-notes-plugin xfce4-notifyd xfce4-panel
  xfce4-places-plugin xfce4-power-manager xfce4-quicklauncher-plugin xfce4-screenshooter xfce4-session xfce4-settings xfce4-systemload-plugin xfce4-taskmanager xfce4-time-out-plugin xfce4-timer-plugin
  xfce4-verve-plugin xfce4-volumed xfce4-weather-plugin xfce4-xfapplet-plugin xfce4-xkb-plugin xfdesktop xfwm4 xfwm4-themes xinit xinitrc xorg-dri-ati xorg-dri-intel xorg-dri-mga xorg-dri-nouveau
  xorg-dri-r128 xorg-dri-radeon xorg-dri-savage xorg-dri-sis xorg-dri-via xorg-drv-ati xorg-drv-cirrus xorg-drv-intel xorg-drv-joystick xorg-drv-mach64 xorg-drv-mga xorg-drv-multimedia xorg-drv-nouveau
  xorg-drv-nv xorg-drv-openchrome xorg-drv-qxl xorg-drv-r128 xorg-drv-radeon xorg-drv-s3 xorg-drv-s3virge xorg-drv-savage xorg-drv-sis xorg-drv-synaptics xorg-drv-video xorg-drv-void xorg-drv-wacom xorg-utils
  xsane xsane-gimp2 yelp zenity
Следующие НОВЫЕ пакеты будут установлены:
  at-spi2-atk at-spi2-core colord empathy-data epiphany-data firmware-crystalhd freerdp-plugins-standard frei0r-plugins gedit-data gnome-icon-theme-symbolic gnome-video-effects gsettings-desktop-schemas-data
  gst-plugins-bad1.0 gst-plugins-ugly1.0 gstreamer1.0 gthumb-data gxmessage kde4-nepomuk-core-common libXevie libarchive13 libat-spi2-core libattica0.4 libboost_system1.53.0 libbs2b libclucene-contribs-lib
  libclucene-core libclucene-shared libcolord libcrystalhd libfarstream0.2 libgavl libgdl3 libgnome-menus-gir libgnome-menus2 libgphoto2_2.4 libgst-plugins1.0 libgstreamer1.0 libgusb libgxps libiniparser
  libjson libkde4base-runtime libmbim-glib libmm-glib libmtdev libnet-snmp30 libnettle libnl3 libnm-gtk libopenblas libpcrecpp libpng15 libpoppler36 libprotobuf7 libpython libqmi-glib libraw libsecret
  libsemanage libsepol libsystemd-daemon libsystemd-login libtbb libtevent libtiff5 libudisks2 libustr libvncserver libvte3 libwayland-client libwayland-cursor libwayland-egl libwayland-server
  libwebkitgtk3-webinspector libxcbutil-keysyms libxkbcommon mono-csharp mono-devel mono-mcs monodis perl-Unicode-Normalize policycoreutils python-module-IPy python-module-audit python-module-distribute
  python-module-nss python-module-py python-module-pygobject3 python-module-selinux python-module-semanage python-module-sepolgen python-modules-unittest rpm-build-mono rpm-build-vala selinux-policy
  vapi-common xfce4-common
197 будет обновлено, 97 новых установлено, 1 пакетов будет заменено, 356 пакетов будет удалено и 0 будет сохранено.
Понадобится получить более 143MB архивов.
После распаковки будет освобождено 1544MB дискового пространства.
Продолжить? [Y/n] n
Прервано.
apt>

gmp-5.1.2-alt2 -> sisyphus:

* Mon Jul 08 2013 Dmitry V. Levin <ldv@altlinux> 5.1.2-alt2
- libgmp10 shouldn't formally obsolete older libgmp (closes: #29152).

Thanks! It's ok now.