to trigger/signal a rebuild for the transition 5.8.8 -> 5.10.0.
The list of packages is computed by finding all packages which end
up having either of PERL5_USE_PACKLIST, BUILDLINK_API_DEPENDS.perl,
or PERL5_PACKLIST defined in their make setup (tested via
"make show-vars VARNAMES=...").
File::Which is a portable implementation (in Perl) of `which', and
can be used to get the absolute filename of an executable program
installed somewhere in your PATH, or just check for its existence.
It includes the command-line utility `pwhich' which has the same
function as `which'.
