Shared directories can now be created independently by the pacakges
needing them and will be removed automatically by pkg_delete when empty.
Packages needing empty directories can use the @pkgdir command in PLIST.
Discussed and ok'd in thread starting at
http://mail-index.netbsd.org/tech-pkg/2009/06/30/msg003546.html
pkgsrc notes:
-modified to use system libz instead of a bundled copy
-disabled the option to create self-extracting combinations of
the executable with a data file. This relies on reliable deduction
of the currrent executable's path which cannot be done in a portable
way, and it doesn't make much sense anyway because that thing needs
a zillion of shared libraries.
