Fixes a display bug seenby ajacoutot@, ok jsg@ and kettenis@.
newer X.Org (2.99.917 or master) version cause corruption on older
machines (X40, i965), probably caused by a bug in our kernel,
under investigation by kettenis@.
2.9.1 is the last version of the intel DDX that supports UMS (User
modesetting), with 2.10 onwards being purely KMS only. As such, this
driver contains backports of almost every correctness or performance
related fix to the rendering layer in later intel drivers. This driver
*REQUIRES* a GEM enabled kernel. it claims to support non-gem mode but
this is essentially unmaintained and due to the way the abstraciton
works is slow, if it works at all (it often does not). You have been
warned.
tested by many many people on tech over the last few weeks.
