- changed rendering of glowing walls so that it doesn't require an additional vertex attribute, just pass the floor and ceiling planes as uniforms.
- rewrote vertex buffer code to require GL_ARB_BUFFER_STORAGE extension.

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.
- add vertex buffer based drawing for all walls and flats.