Log Message:
Update Mesa and friends to version 5.0, using patches provided in PR pkg/19302.
At the same time, move Mesa and friends to LOCALBASE rather than X11BASE, so
that they can be installed regardless of XF version.  Introduce MESA_REQD variable
that can be set to 5.0, thus allowing systems with XF4 to indicate that the
provided version is not good enough.

All packages using Mesa, MesaLib, glu or glut will get a PKGREVISION bump
over the next few days.