This is a huge patch, including:
* add a LitRenderModifier abstract base class for RenderModifiers with
shadow+light
* add LitRenderModifiers for all types of models
* add STREAM_TEXGENTOUV1 to request generation of shadow map texcoords
for models
* create facilities to pass the texture matrix from the
RenderModifier (fragment stage) to the ModelRenderer (vertex stage)
* split ambient and diffuse terms of lighting until further down in the
pipeline; this is necessary since shadowed regions receive only
ambient light
* small improvement in how RenderPathVertexShader scales to a greater
number of vertex shaders
This was SVN commit r3690.
