This was causing problems with R300G. The GPU supports only limited
GLSL and seems not to be up to rendering the scene appropriate. So
let's better disable the OpenGL 2 branch for such GPUs. If the user
really wants to use it, there is the GLES backend which does not
check for limited GLSL.
BUG: 274457
CCBUG: 274607
FIXED-IN: 4.7.0