installing buildlinkX11.rules as X11.rules via a symlink to ensure that
buildlinkX11.rules gets used in place of X11.rules everywhere. This should
fix pkg/13638 by Martin Husemann <martin@duskware.de>.
addition of the xmkmf script from the XFree86-4.0.x distribution, which
understands passing -D options through to imake. Update the dependency
on buildlink-x11 in bsd.pkg.mk for packages using USE_BUILDLINK_ONLY to
>=0.5. Also, if USE_BUILDLINK_X11 is set, then refer to ${BUILDLINK_DIR}
for location of X headers and libraries.