Ensure postfix is largefile aware on SunOS.

Bump PKGREVISION.
Updated mail/postfix to 2.9.6nb4
After including builtin.mk files, go through BUILDLINK_TREE in tree order
and force USE_BUILTIN.pkg=no for packages that depend on packages where
USE_BUILTIN.pkg is no. The names of any such packages are accumulated in
the variable FORCED_PKGSRC for reference; this is currently undocumented
and could be dropped in the future.

This makes it a lot safer to install pkgsrc versions of selected X
libraries without switching wholesale to pkgsrc X; however, other
issues may still exist and caution is still advisable.

As seen on tech-pkg.

Also note: this may affect the builds of packages we don't realize are
affected and that haven't been revbumped. If you find one, let us know
so we can bump its version (or do that yourself) -- most likely this
change will produce in working, properly-linked packages that were
previously broken, but if problems arise please speak up.
Remove special-case dependency-checking logic now handled by the
general solution I checked in in bsd.buildlink3.mk.