[Pixman] [PATCH v9] Implement PIXMAN_FILTER_GOOD/BEST

[spitzak at gmail.com]

Changes from previous version:

- Passes make check (previous one crashed in stress-test)
- Negative subsample_bits sets it to appx log2(-n/scale)
- Scale demo changed to default to the GOOD setting and allow negative subsamples
- Some adjustment of the subsampling in GOOD/BEST

Compatibiliy notes:

For the default filter of GOOD this produces the same BILINEAR result for any scale 
greater than 3/4, and also for a scale of 1/2 if there is no rotation or translation.
For BEST the output is changed for all transforms other than the identity. For
other filter settings the result is unchanged.

These changes match those done to Cairo about 1.5 years ago, with the same amount
of incompatability. Making these changes will allow Cairo to use pixman directly
rather than generate it's own filters.