Subtle dedupe improvement for the perl5 system

There are plenty of cases where the only thing that differs between
the various builds are the dependencies.  For example, we may use
Exporter from CPAN (5.70) while the 5.20 core has 5.71.  This means
that the non-5.20 builds end up with a dependency that the 5.20 build
doesn't have since it gets a newer version from the core.

We will handle the dedupe case specially when the only thing that is
different are the depends.conf files.  If everything else is the same,
then we will dedupe everything except lib/efs, which we will leave
behing in the exec tree.  This at least dedupes the code, man pages,
and binaries.

Also, we ignore the paths to perl when calculating the checksum of the
bin contents, since we embed the interpreter line into them
automatically.

We will use the most recent build (based on sort order, really) to try
to pick up the latest 5.20 builds of everything, which get the latest
version of auto-generated man pages, and bin contents which run with
5.20 instead of the oldest perl we have.
fixup! Subtle dedupe improvement for the perl5 system
fixup! Subtle dedupe improvement for the perl5 system
fixup! Subtle dedupe improvement for the perl5 system