pixmap into temporary offscreen storage. Subsequent UploadToScratch may
    clobber the data of previous ones. This allows hardware acceleration of
    composite operations on glyphs.
- Add a new UploadToScreen kaa hook for doing the actual moving of data to
    framebuffer. This would allow us to do things like hostdata blits or
    memcpy to agp and then blit.
- Add an UploadToScreen on ATI which is just memcpy, but which will be
    replaced with a hostdata blit soon.
- Add UploadToScratch on ATI and reserve 64k of scratch space. This
    provided a 3x speedup of rgb24text on my Radeon.