Log Message:
Alter Mesa/GL packages so that they may always be installed if
X11PREFIX != X11BASE (xpkgwedge is installed).  Introduce a new variable
MESA_REQD that defaults to "3.4.2" and represents the version of Mesa/GL
needed by a package.  MESA_REQD is intended to be used by package Makefiles
or by buildlink2.mk files.

It should now be possible to update this package to the latest release
(5.0), and have it work on:

	* XF86-3.x with or without xpkgwedge
	* XF86-4.x with xpkgwedge