first set of new APIs + convert server to use them

[Dave Airlie]

This set of patches provides new APIs for converting scrn->screen and vice
versa, and converts most of the low-hanging fruit in the X server to use
them. Further changes are needed, but it would be good to get started,
and we can start converting over a lot of the code in the drivers.

The second set of patches adds new GlyphPicture accessors instead of directly
accessing global arrays, it converts render/exa to use them.

These are just new API and provide defines to allow servers to define
fallback versions in a simple header file.

Dave.