Fixed wrong fog flag being used (must be GLS_FOG) in RB_SetupFog().
R_SetupFrustum():
- Use skybox farplane and farplane bias
- RB_SetupFog() is now the only function who handle fog activation
RE_RenderScene():
- Set renderTerrain, skybox_farplane and farplane_bias parameters
- Set color overrides
- Use farclip when necessary
RB_StageIteratorLightmappedMultitextureUnfogged(): Fixed issue with fog being reset