Drop GLcore dependency from glx module.
Work around double destroy case and add DRIUnlockedCallback() function.
New files, lots of code coming from GL/mesa/X/xf86glx.c and the libGL
loader code.
Port all changes from the (monolithic) accelerated_indirect-0-0-1 branch to
the modular trunk. This will break the Darwin and cygwin builds. Other
than the changes to symlink-mesa.sh and the various Makefile.am files,
to code is identical to what's in the branch.
Reviewed by: airlied, krh
