Add comments that describe the range of Q_random and Q_crandom

Fuma wants them. The functions themselves aren't exactly descriptive at a glance.
Set cl_renderer GL if GL3 crashes during shader compilation.

In a release build, GLSL shader compiliation usually means that the hardware does
not support GLSL shaders and should rely on vanilla instead.
Fall back to vanilla renderer if OpenGL version < 2.1

OpenGL 2.1 introduced GLSL version 1.20 which introduced a few features that we use
We also specify #version 120 in the shader text
Print a few short interesting bits of OpenGL information by default to help with debugging user issues
Remove a few useless or duplicate things from q_shared.h
give out the current used entity count in /entitylist to get actual entityamount instead of the poolsize