Mesa-8.0.1 and freeglut

[Jeremy Huddleston]

mesa stopped including an implementation of glut with their releases, so the latest version that I just pushed into dports no longer provides libglut.

freeglut is a new port which fills this void left by mesa.  Unfortunately, it's difficult to determine by looking at an individual port if its mesa dependency is a requirement for mesa (libGL, libGLU) or freeglut (libglut).  It doesn't look like anything in our tree actually needs glut (indeed most hits for glut are --disable-glut), so I don't think this will be a big deal, but I thought I'd call it out in case there's something I missed.

If you find a port failing to build because it can't find libglut, please add a dependency on port:freeglut.

Thanks,
Jeremy