ast driver patches

[Dave Airlie]

It appears you are reverting the changes made by Adam Jackson in

http://cgit.freedesktop.org/xorg/driver/xf86-video-ast/commit/?id=d07efd4f80754d82540ebdaa7c2a062e68f229b9

this means the driver won't work correctly against the latest X server
without crashing.

It would help it the commit message contained some information on what
the segmentation fault under Xen looked like, and why the changes fix
it.