Blender Git Loki

Applying patch #25898 by Shinsuke Irie for rendering total external reflections
* Tracing objects with IOR < 1.0 (like air bubbles under water) wasn't working correctly as a refraction was always assumed to be the first thing that happens for transparent materials.
* This fix is ok, but the fact that the internal renderer is not a physically based one is starting to show, as for example blurred reflections in this case are not really possible nicely without some slightly heavier modifications to the ray code.
* Also some cleaned up logic and better comments for my previous total internal reflection commit.