cleaning up GLSL code

cleaning up GLSL code
moved GLSL shader setup to gl_rmain.c and made it more general, not specifically lighting shaders
cache locations of GLSL shader variables for faster access (instead of looking them up every time it renders something)
GLSL shader reworked to support deluxemap rendering and lightmap rendering, to be used in the future
merged glsl/light.frag and glsl/light.vert into glsl/default.glsl using VERTEX_SHADER and FRAGMENT_SHADER defines to differentiate parts of it

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@6121 d7cf8633-e32d-0410-b094-e92efae38249