Blender Git Loki

Patch #7081:
Submitted by: David Bryant

This patch adds 2 new drawtypes for empties (circle draws a 2d-circle on the x-z plane, and cube draws a regular cube), and allows empties to be used as custom bone shapes.

I've modified the patch a bit to fix up weird formatting, optimising the circle-drawing method, but the cube-drawing function has been maintained. In the process, I also moved the mesh-specific code in draw_object_instance to draw_object_mesh_instance so that empties can be used by whatever else might use draw_object_instance too.