Package missing Conflicts: imp in .spec. Without this option we have package
intersections during dist-upgrade:

$ apt-get install horde-imp
...
file /var/www/html/addon-modules/horde/imp/templates/prefs/trashselect.inc from
install of horde-imp-4.1.4-alt2 conflicts with file from package imp-3.2.6-alt1
file /var/www/html/addon-modules/horde/imp/templates/search/javascript.inc from
install of horde-imp-4.1.4-alt2 conflicts with file from package imp-3.2.6-alt1
file /var/www/html/addon-modules/horde/imp/templates/search/main.inc from
install of horde-imp-4.1.4-alt2 conflicts with file from package imp-3.2.6-alt1
file /var/www/html/addon-modules/horde/imp/test.php from install of
horde-imp-4.1.4-alt2 conflicts with file from package imp-3.2.6-alt1
file /var/www/html/addon-modules/horde/imp/view.php from install of
horde-imp-4.1.4-alt2 conflicts with file from package imp-3.2.6-alt1
E: Error while running transaction

Steps to Reproduce:
1. apt-get install imp (from old Sisyphus archive)
2. apt-get update (to current Sisyphus)
3. apt-get install horde-imp
Actual Results:  
conflicting files in packages.

Expected Results:  
seamless upgrade/or plain conflicts between packages.