channels to link texture to.
The amount of code changes seems large, but is mostly getting rind of
hardcoded values (6 and 8) for channels, replacing it with MAX_MTEX.
Further did some fixes;
- Ipo for Lamp showed too many mapping channels
- Texture MapTo buttons for lamp missed the slider to blend texture color
- Lamp texture mapping "View" only worked for Spot, now it uses lamp-
view vector for all types. (Nice for projections!)