i've been using pkgsrc for a while and quite like it.   however,
as time as gone on my pkgsrc/distfiles directory has accumulated
a large number of old versions of packages that have been updated.

for example, i've now got 4 copies of libpng, only one of which
i need or use:

    xxx> ls pkgsrc/distfiles/libpng*
    pkgsrc/distfiles/libpng-1.0.11.tar.gz   pkgsrc/distfiles/libpng-1.0.3.tar.gz
    pkgsrc/distfiles/libpng-1.0.12.tar.gz   pkgsrc/distfiles/libpng-1.0.6.tar.gz
    xxx> 


is there a pkgsrc program or make target that i can use to delete
old, obsolete, or unused distfiles from my system?   i couldn't 
find anything documented that does what i want...


chuck