Bug#651227: Compositing unuseable with Radeon r300

[Thomas Viehweger <patchesThomas.Vie@web.de>]

I retried with 4:4.8.4-3 but got similar bad results than a year ago:
> glxgears 
Running synchronized to the vertical refresh.  The framerate should be
approximately the same as the monitor refresh rate.
62 frames in 5.0 seconds = 12.369 FPS
64 frames in 5.0 seconds = 12.778 FPS
...

from glxinfo:
OpenGL vendor string: X.Org R300 Project
OpenGL renderer string: Gallium 0.4 on ATI RS690
OpenGL version string: 2.1 Mesa 8.0.4
OpenGL shading language version string: 1.20