Blender Git Loki

Fix T41005: Seemingly random crashes with cycles rendering
Fix T41013: OSL and Crash
Fix T40989: Intermittent crash clicking material color selector

Issue was caused by not enough precision for inversion threshold.
Use double precision for this threshold now. We might want to
investigate this code a bit more further, stock implementation
uses doubles for all computation. Using floats might be a reason
of bad rows distribution in theory.