BUILDLINK_PREFIX.<pkgname>. This allows buildlink to find X11BASE packages
regardless of whether they were installed before or after xpkgwedge was
installed. Idea by Alistair Crooks <agc@pkgsrc.org>.
FOO_REQD=1.0 being converted to foo>=1.0, one can now directly specify
the dependency pattern as FOO_DEPENDS=foo>=1.0. This allows things like
JPEG_DEPENDS=jpeg-6b, or fancier expressions like for postgresql-lib.
Change existing FOO_REQD definitions in Makefiles to FOO_DEPENDS.
linked from a particular package, and add a pre-configure target to
the buildlink.mk file to more painlessly use buildlink.mk files. A
${BUILDLINK_TARGETS} variable still exists in case a package _must_
define NO_CONFIGURE.
