EXA fix for xserver 1.5

[Michel Dänzer]

I'm proposing to merge the following fix from the master branch to the
1.5 branch. Release folks, please review and (N)ACK.

Commit 6c95fae1e9d6b0eb64bc78eced05a6e9f5faf02e ('EXA: Offscreen memory
eviction improvements.') fixes a regression of previous 1.5 backport
2e4b72dd8485df1f89ce4533a5778514ad1fc917 ('EXA: Improve the algorithm
used for tracking offscreen pixmap use.'): unallocated offscreen areas
were now considered to have a non-zero eviction cost. According to
http://bugs.freedesktop.org/show_bug.cgi?id=15513 the latter introduced
corruption with the radeon driver which the latter fixes, and although
the exact reasons remain kind of a mystery, the above commit fixes a
clear regression and helps...

Commits 26c1801a27b81fdd988d5bd210ba0e76ecc274ae ('EXA: Update
sys_pitch/fb_pitch in exaModifyPixmapHeader.') and
3f081b4de55e1378728a24d069bf06575ffca2d8 ('EXA: Set
pixmap->accel_blocked on the screen pixmap, too.') look like they might
be worth backporting as well - they seem important for the intel driver
at least - but I'll defer to Tilman for assessment of their benefits vs.
risks.


-- 
Earthling Michel Dänzer           |          http://tungstengraphics.com
Libre software enthusiast         |          Debian, X and DRI developer