Comparing the set of installed files with the package database

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

Is there a sane way to compare the set of files present unter /usr/pkg with 
the package database?
I would like to identify files left over from incomplete de-installations.
I tried to compare the (filtered) output of pkg_info -L with that of a find 
(/usr/pkg -path /usr/pkg/etc -prune -or -type f -print);
the main problem appears to be that some symlinks are listed in the pkg_info 
output while some (mainly those from Perl) are not.