[cairo] Faster gradients patchset, take 2

[David Turner]

Hello,

here's another patchset to speed up gradient rendering. It includes the previous one that sped up the radial
case, as well as a simple technique to speed up the pretty common case where all color stops are opaque, which
saves quite a lot of per-pixel computations.

  http://david.freetype.org/cairo/faster-gradients-2.patchset

Apparently, this means speed-ups of up to x2.04 for radial gradients, and x1.67 for linear ones

Enjoy,

- David Turner
- The FreeType Project  (www.freetype.org)