Switched embree to use catmull-rom curves
Switched embree to use catmull-rom curves

The latest versions of Embree support Catmull-Rom splines
which use less memory than the previously used Hermite splines.
The representation is also much closer to Cycles own data structures
and can hopefully be unified in the future for more memory savings.

Memory savings using Victor benchmark scene:
Compared to previous Embree: ~400MB
Compared to Cycles' native BVH: ~1GB

tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird