Blender Git Loki

GPU Buffers:

This commit begins implementation of the idea about hidden face
separation outlined in

http://code.blender.org/2015/06/optimizing-blenders-real-time-mesh-

We split hidden and visible faces to different parts of the triangle
buffer.
Mapped drawing will now skip iterating through hidden polys.
Of course the final target, when all derived mesh types use
VBO sorting, is to skip checking for hide flag per face
completely. All faces will be pre-sorted anyway and we'll
be able to draw them with one draw call.