Blender Git Loki

Cycles: Support CUDA Graphics Interoperability

Allows to update GPUDisplay using CUDA without need to copy pixels
from GPU to CPU and back to GPU.

Pretty much refactoring the old code to fit into the new GPUDisplay
and PathTraceWork.

Rendering on CUDA Titan V which is the display card here is about 10%
faster vieweport rendering of simple scene compared to the round trip.

The compute device RTC6000 is 17% slower that the round trip.
Would not consider this a stopper for this change as the similar timing
difference can be observed in the old DisplayBuffer style of drawing.