Mesa3 removal

[Eric Anholt]

I removed the Mesa3 port today.  It's been replaced by two ports:
graphics/libglut and graphics/mesagl.  The graphics/mesagl things are
provided by XFree86-4 and thus unnecessary for XFREE86_VERSION=4.

This means that USE_MESA, which has meant "provide libGL and libglut"
can be changed to either a LIB_DEPENDS on graphics/libglut for those
ports that need libglut, or USE_GL=yes, which depends on graphics/mesagl
or x11/XFree86-4-libraries depending on XFREE86_VERSION.  I have no
plans to change USE_MESA usage across the ports tree, but at least new
ports should probably not use USE_MESA.

-- 
Eric Anholt                                eta at lclark.edu          
http://people.freebsd.org/~anholt/         anholt at FreeBSD.org