Now we use the software path for YUV, and CoreGraphics for 2D stuff.

There are several other 10.6 fixes in here, too...now we can build a 64-bit
SDL for Snow Leopard!

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%403838