FindPackage() should prefer virtual dependencies as they provide more
semantics.  E.g. /usr/bin/perl dependency exposes that perl interpeter
is in use, while dependency on perl-base is not that meaningful.

I think it's easy implement reverse lookup against rpm database:

$ rpm -q --whatprovides /usr/bin/perl
perl-base-5.8.7-alt2
perl-base-5.8.7-alt2
$ rpm -q --provides perl-base-5.8.7-alt2 |grep /usr/bin/perl
/usr/bin/perl
$

But there's a problem with reverse lookup using contents_index:

$ awk '"/usr/bin/perl"==$1' ~sisyphus/i586/base/contents_index
/usr/bin/perl   perl-base
$

Maybe we should alter how contents_index is generated so that it has both
/usr/bin/perl perl-base
/usr/bin/perl /usr/bin/perl
Steps to Reproduce:
$ rpm -q --whatprovides /usr/bin/perl
perl-base-5.8.7-alt2
perl-base-5.8.7-alt2
$ RPM_BUILD_ROOT=/tmp . /usr/lib/rpm/find-package && RPM_BUILD_ROOT=/tmp
FindPackage /tmp/script /usr/bin/perl
Actual Results:  
perl-base

Expected Results:  
/usr/bin/perl