- separate location installed binaries from non-binaries (previously
  installed package.conf was in $(libdir)/extra-bin).

- remove v_Path_Perl so that we don't accidentally wire-in the location of
  perl on Unix systems.  It wasn't actually used anywhere.

- minor non-functional cleanups and comment fixups.

- We still look for package.conf twice; I haven't done anything about
  this yet.