regression in rotation since 77c7a64e8885696665556c9fbcb3cffb552e367a

[Dave Airlie]

Had this reported internally and have confirmed, and as matrix and
transforms is above my station, I'll drop it here.

Setup laptop with LVDS + VGA in right-of, rotate VGA, notice one pixel
overlap of gnome panel onto VGA from LVDS or any window in the last
pixel of the LVDS.

With this patch reverted we no longer see that pixel, but we do seem
to lose the one of the end of the screen.

Dave.