Alternate zfreeze solution

Provides skybox depth fix for RS games and eliminates shadow z-fighting.
Mario Tennis gimmick courses are still an issue, but I think can be
fixed if we can adjust z-depth bias.  Changes to PixelShaderGen, so
clear ShaderCache to test please!  Was only able to test RS games, Mario
Tennis and Mario Strikers.

Additional work/testing to determine better state setting logic in
Render.cpp