Blender Git Loki

Cycles: Implement record-all transparent shadow function for GPU

The idea is to record all possible transparent intersections when
shooting transparent ray on GPU (similar to what we were doing on
CPU already).

This avoids need of doing whole ray-to-scene intersections queries
for each intersection and speeds up a lot cases like transparent
hair in the cost of extra memory.

This commit is a base ground for now and this feature is kept
disabled for until some further tweaks.