Add support for DepthComponent FBOs (a single attachment with a depth buffer).
Shader will now parse more sampler types (mostly untested, but sampler2dshadow works).
Shader now preallocates a float[] for using SetValue(Matrix4 param), which should only be used by one active thread.
Get rid of TextureParam enum and use the new TextureParameter enum instead (part of GlEnum.cs).
Modify the Gl library to accept TextureParameter for TexParameteri, as well as int.  Update all methods.
Sometimes a Frustum might be provided with a pre-computed modelview * projection matrix.