Blender Git Loki

OpenSubdiv: Initial support of tanged spaced normal maps

Made it so tnagent space is being calculated from GLSL
instead of using CD_TANGENT layer (which is missing for
the OSD meshes).

For now used real basic tangent space calculation, which
is _really_ average and only looks ok-ish with high
enough number of faces.

This is to be improved further with either using different
tangent space calculation or using some sort of evaluator
from OSD (seems they've got some code for this, but it's
not that trivial to hook up for tests because of the way
how our GLSL pipeline is constructed).