The NVfp2 control flow uses the D3D syntax, and doesn't need the inversed
branch condition we're using in the vertex shader.

I don't like that I have to do this because the posFixup is in all
vertex programs, so its at the same position and could be loaded
globally.  Unfortunately, there are only 256 env parameters usually,
which makes it impossible for any shader to use c256, even if it does
not use indirect addressing, and so we can't claim 256 constant
support.