Don't calculate world surface fog numbers each frame

Put hard coded global fog at index 1. Make surfaces use it at load time instead of calculating fognum (defaulting to global fog if enabled) each frame.

Fixes fog at beginning of q3dm4.
Don't calculate fogDistanceVector before checking if fog is enabled
Don't use GLSL shader with fogging if surface uses (disabled) global fog
Sync GL2 CGEN_FOG with GL1 CGEN_FOG