Log message:
Simply and speed up buildlink3.mk files and processing.
This changes the buildlink3.mk files to use an include guard for the
recursive include. The use of BUILDLINK_DEPTH, BUILDLINK_DEPENDS,
BUILDLINK_PACKAGES and BUILDLINK_ORDER is handled by a single new
variable BUILDLINK_TREE. Each buildlink3.mk file adds a pair of
enter/exit marker, which can be used to reconstruct the tree and
to determine first level includes. Avoiding := for large variables
(BUILDLINK_ORDER) speeds up parse time as += has linear complexity.
The include guard reduces system time by avoiding reading files over and
over again. For complex packages this reduces both %user and %sys time to
half of the former time.

Log message:
Merge cube-native-xorg, so that pkgsrc-current can be used with the native
X.Org found in NetBSD-current.

Thanks a lot to all who helped, especially Matthias Scheler who did
repeated tests on Mac OS X and older versions of NetBSD to make sure the
support for those platforms wouldn't be broken (or at least, not fatally,
as I would still expect a few hiccups here and there, because there is
only so much one can test in such limited time).

On the infrastructure side, this branch brings pkgconfig-builtin.mk, in
order to write very easily new builtin.mk files.  It can actually handle
more than just pkgconfig files, but it will provide a version if it finds
such a file.  x11.builtin.mk has also been made more useful and now all
existing (and future!) native-X11-related builtin.mk files should include
it.

Log message:
Switch master site to MASTER_SITE_XORG.

Log message:
Import videoproto-2.2.2 from pkgsrc-wip:
Video extension headers from modular X.org X11 project.