Blender Git Loki

- added Mesh.MVert(); can now create 'thick' vertices which don't wrap mesh
- implemented slice operations (get/set) for vertex list; allows script
writers to manipulate lists of vertices (using 'thick' vertices)
- fixed problem in mesh.faces.extend() which allowed the creation of
"Eeekadoodle" faces
- added mesh.update() method; (possibly) temporary fix to allow updating DAG