[Pixman] Compute flags at validation time instea

[Soeren Sandmann]

Hi,

I intend to land the branch here:

        http://cgit.freedesktop.org/~sandmann/pixman/log/?h=more-flags

fairly soon. It contains various optimizations:

- Do the flags and extended-format computation at validation time
  instead of composite time

- Eliminate _pixman_image_is_solid() and _is_opaque() in favor of two
  new flags.

- Turn the need_workaround boolean into another flags

Most of it should be fairly straight-forward, but as always, reviews
appreciated.



Thanks,
Soren