If glColorMaterial is set to track current color and none is supplied,
it gets disabled.
glMaterial is reset when I think it is necessary.
Slow mode now has defaults for when fvf parms are not supplied (as per
fast mode).
Slow mode now sets up the specular color (forgot that bit previously,
I think!).
Trace now lists the front, back and stencil buffers for ease of
debugging.