Blender Git Loki

Step one in bringing back Yafray Render in Blender. Need someone else
to take over now, but I'm available for help. Main notes for completing:

- Yafray module uses old global R all over... is now a pointer handle.
It can be temporally bypassed by straight copying, which I do now.

- I am not sure in what pixel format Yafray renders... Blender now only
uses float buffers. In the code, marked with XXX I've added the
rudimentary code for retrieving buffers.

- This integration will skip compositing when Yafray render is used.