Where possible, symbols have been made static, prefixed with glsl_/GLSL_ or
moved into the code shared by all renderers. This will make doing plugins
easier but done now for link testing. The moving was done via the gl
commit.
The plan is to do interpolated sprites based on a discussion I had with
LordHavoc about them: blending between the two sprite frames. He didn't
mention it, but it looks like blending between the sprite frames' verts is
necessary too.
