[PATCH 0/5] mioverlay cleanups

[Adam Jackson]

One of the nasty bits about getting backing store's Always mode working
again is the asymmetry between map and unmap, namely that sometimes
pWin->valdata is a struct and sometimes a magic out-of-band value
indicating unmap.  This would be fairly easy to clean up except for the
overlay visual code in mi, which has to maintain a shadow clip list so
it can repaint transparency keys.  Unfortunately the only extant user
of mioverlay is the nvidia driver on workstation Quadros, so this is a
little hard to test.  (fglrx also has overlay visual support, but they
don't appear to be using mioverlay to accomplish it.)

Also nobody has materially touched that code in something like 12 years,
and it's not what you would call "commented", or "obvious".

This (compile-tested only) series attempts to eliminate mioverlay's
internal use of UnmapValData.  It probably makes x11perf's valtree
benchmarks marginally faster since we're no longer passing around dead
variables, and it should be functionally equivalent.

- ajax