Improved a bit on MapMesh data handling.
Pulled MapMesh model handling together.
Allow MapMesh data to linger.
Handle MapMesh surfaces in the new data system as well.
Merge branch 'core'
Only indicate GLSL support if GLSL version is >= 1.20.
Merge branch 'core'
Removed debug message.
Rationalized the division between TexDraw and TexClip a whole lot.

While I find it hard to believe that I would have done all that just by not
thinking, I sure can't think of any Earthly reason why it should exist, and
removing it certainly doesn't seem to have any ill effects either. It even
fixed the alpha-coverage application bug.
Allow modifying the mains of shader contexts with more arbitrary code.
Added the GLSL discard statement.
Added proper GLSL support for tex-clipping.
Merge branch 'core'
Switched shuse for a more extensive progmode setting.
Merge branch 'core'
Fixed PView cls profiling.
Keep global, static variables with current modkeys, just for debugging purposes.
Allow unambiguous abbreviations in enum GL-settings.
Added explanatory comment for the future.
Split the RenderState into a RenderContext for separability.