More 24bit optimizations (was: a just another stupid newbie :)

[Keith Packard]

Around 5 o'clock on Dec 15, Jaymz Julian wrote:

> hrm, it actually worked for me in fbCompiositeGeneral as well, but I guess it
> was just two bugs cancelling each other out or something :).

You might check out fbCompositeGeneral and see how hard that would be to 
fix; it might be quite easy, and that would be useful as we'd eliminate a 
bunch of weird code in fbComposite.

-keith