glamor-server subset patch bomb

[Eric Anholt]

keithp said he was tired of the glamor stuff trickling in and wanted
to just review it all at once and be done.  I know I hate reviewing
giant patch series, but who am I to argue with someone who says they
want to do more review?

This series fixes a bunch of CopyPlane XTS tests in Xephyr, thanks to
the GC prepare fixes if I remember right.

There are a few patches that used to be in glamor-server that I
dropped.  Some were performance ideas that didn't produce measurable
results (yet -- in one case, it's that I think I misplaced a spans
patch I used to have, which was a prereq for another change being
useful).  Others just regressed things.  So, if you've got your own
glamor branches based off of my glamor-server, be careful not to carry
that junk around.