Blender Git Loki

Initial VBO code for GPU subsurf.

This commit adds a few generalizations to the VBO
code so that modifiers can create and populate their own GPU objects.

The VBO code originally supported CDDerivedMesh only. The design moves slightly
towards the viewport refactor where the rendering system requests data from the
modifiers.

In this commit only basic support for vertices and normals is provided and
some features from blender's VBO system, suchs as mapping to original faces,
unique element indices for vertices and loose vertex/edge support are missing.
Also, the quick navigation feature of the subsurf modifier won't be supported
for now.

What we do have is full support for solid shading with multiple materials,
flat/smooth shading and a big performance boost.