[PATCH 0/8] Implement backing store's Always mode (v2)

[Adam Jackson]

This is juggled around a bit from the previous series.  I've not made any
real attempt to annotate the patches for what changed, sorry.  This is
still unfinished, but it's closer than before.  Composite now handles
exposure suppression itself instead of hacking it into mi.  I took Keith's
advice and moved setting ->paintable to DIX.  And I probably broke
mioverlay since I changed the unmap path to not use an out-of-band marker
in validation.

This does regress XMapWindow/13 and XMapSubwindows/12 in xts, so it's
clearly not right yet, but again more eyes would be appreciated.

- ajax