[Pixman] [PATCH pixman] V6 implement PIXMAN_FILTER_GOOD/BEST

[spitzak at gmail.com]

This is identical to my previous series of patches except rebased atop the
current git master. Note that all patches except the last one are bug fixes
to produce correct filters, and do not produce any changes in pixman output.
IMHO the first 14 patches should be applied asap.

The last patch changes the output when GOOD or BEST filters are used and 
images are scaled down. Output is nearly identical to what cairo is 
producing now, but I did some minor tweaks to cutoffs between filters 
and handling of very small scales. This one also detects a few more 
instances where nearest or bilinear can be used as a fast path.

With all of these applied, the filter generation can be removed from cairo as
pixman will do it. The fallback to image for the X11 backend could be removed
if it is known the X11 server is using this new version.

This is also a necessary step in order to introduce 2-pass image filtering
to pixman. Currently software such as Cairo cannot use the filtering in
pixman and this means it will bypass any such improvements.