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
WRKSRC. LIBTOOL_OVERRIDE defaults to "libtool */libtool and */*/libtool,"
meaning that, in most packages, there's no need to set it.
So: Nuke tons of LIBTOOL_OVERRIDE=${WRKSRC} and adjust a few
SHLIBTOOL_OVERRIDEs (remove ${WRKSRC} from them).