Blender Git Loki

Bugfix #3608

More bump issues... Env made very nice examples, but all of it quite nasty
to solve.
Three improvements I found nevertheless:

- bug in mipmap code for bump gave errors in one derivate, causing aliasing
- when Image texture option "Clip" was used, the imagetexture function
returned wrong value, causing the caller to create own normal based on
color (zero!).
- Mipmapped bump now also interpolates the samples (never did this...)