Revert "Switch to KeithP's xorg/xserver tree for extra glamor"

This reverts commit 4c7ec11c3b071b1b4c75c6b68598b0a6c962063e.

KeithP's fork of xorg/xserver is no longer needed, as all current
commits are happening in git://anongit.freedesktop.org/xorg/xserver.
This ebuild is rapidly becoming superfluous since it is now essentially
identical to the x11 overlay's ebuild.  Will probably remove.
Rebase media-libs/mesa-9999 on x11 overlay's

FireBurn is dead, this (if it continues to exist) needs to be migrated
to robinkverlay.  iXit's repo is sort of quiet right now, I don't need a
spiffy D3D9 state tracker at the moment, and all the exiciting Radeon
VCE and OpenMAX work is happening in fd.o Mesa master.  Changed the name
to -r1, too, since =media-libsa/mesa-9999 has GX86 multilib support.
So, yeah...