Blender Git Loki

Added new operators for "MapTo" panel as suggested & partially coded by
Kent Mein. So next to the mix, mult, add, sub we have now:

- Div: divides by texture color
- Screen: is like Mult, but works opposite (makes lighter)
- Diff: the difference between texture color and material
- Light: if texture is lighter it shows (per component)
- Dark: if texture is darker it shows (per component)

Next step: add this for specular and mirror, and the other channels...
I commit it now because it also fixes error in previous commit.