The overriding of the color mode uniform in the default model effect
wasn't working. It's difficult to override the individual properties
of techniques, especially if their names aren't unique. So, I changed
the model-default effect to use a parameter for the color-mode
uniform; material-off.eff and material-diffuse.eff override that.
Use two-pass rendering for some shaders to reduce the cost of expensive shaders.
Implement some material animations using a shader uniform.
Eliminate use of gl_FrontFacing. It's too buggy on ATI/ Macintosh.
