After thinking about it for a day or so I believe it's the best option to remove all compatibility code because it's a major obstacle for a transition to a core profile.
- disable GL_ARB_buffer_storage when a -glversion parameter less than 4.0 is given. According to the spec this extension requires 4.0 so if emulating something lower it should not be used.
- remove thing color from lighting calculations.
- implement alpha textures and inverse sprites for infrared as texture modes. This still requires some handling for the alpha texture mode for non-shader rendering because there is no way in the fixed pipeline to do it. The inverted texture effect can be done with a texture combiner.
- fixed: ThingColor for sprites was set in the wrong place. It must be in the Process function, not in the lighting calculation.
- added functions for isolated calculation of sprites' dynlight color.
This means it won't work anymore on anything that doesn't support OpenGL 4.0, but I don't think this is a problem. On older NVidia cards performance gains could not be seen and on older AMDs using the vertex buffer was even worse as long as it got mixed with immediate mode rendering.
- removed gl_vid_compatibility. With the bump to 1.4 no hardware requiring this flag is supported anymore.
- disabled 16 bit framebuffers for the same reason. As a conseqence all code for rendering without stencil could also be removed.
