Don't dither the alpha channel.
Don't dither the alpha channel.

git-svn-id: 763a368b42d23a8c112339c16f7e9c1b0ab7c9a5@526 8a90861a-4eca-46d5-b744-240ff16d0c4d

WilliamFeely/dxgl,WilliamFeely/dxgl,WilliamFeely/dxgl,WilliamFeely/dxgl