small crash fix
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.
Added a TexGL function for fetching the current contents as an image.
Merge branch 'core'
Fixed enum-setting bug.
Merge branch 'core'
Added modularly selectable redirection of rendering into a configurable FBO.
Extract a common orthostate class and use it for redirected framebuffers as well.