[cairo] upcoming changes to glitz and cairo

[David Reveman]

I've now committed all changes to glitz. A new snapshot of glitz (0.1.4)
is available for download.

I've also committed the changes needed to make cairo's gl-backend work
well with software multi-sampling. The previously mentioned gradient
pre-multiply fix has also been committed. I wasn't fully happy with the
gl surface image caching, so none of that code have been committed. It
was working quite well, but I think it could be solve in a better way.
The same sort of image cache will be useful for the xlib and xcb
backends when XRender extension is missing. So a general "cached image
fall back", which any backend can use, is probably a much better
solution.
 
-David