- Mike Gist:   - Enhanced the fog shader snippet to support alpha fog.   - Implemented CS_FOG_MODE_LINEAR in the fog shader snippet. It supports a linear (duh) increase of fog density from the fogFadeStart to the fogFadeEnd  (at which point the density is that which is specified). If a fogLimit is given, anything further away from the origin than this is fog-free.
- Mike Gist:
  - Enhanced the fog shader snippet to support alpha fog.
  - Implemented CS_FOG_MODE_LINEAR in the fog shader snippet. It supports a linear (duh) increase of fog density from the fogFadeStart to the fogFadeEnd  (at which point the density is that which is specified). If a fogLimit is given, anything further away from the origin than this is fog-free.

git-svn-id: 28d9401aa571d5108e51b194aae6f24ca5964c06@29926 8cc4aa7f-3514-0410-904f-f2cc9021211c

crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS,crystalspace/CS