Blender Git Loki

Experimental feature, multires apply base, as suggested by renderdemon

* Attempts to fix the "spike" problem with multires
* For example, take the grab brush and pulling a large chunk of the mesh around will create ugly spikes at lower levels
* Another problem is that a multires mesh heavily changed in sculpt mode will still have the original shape in editmode, which might not be very useful
* Solution here is a new operator "Apply Base" that modifies the mesh to conform better to the sculpt multires mesh.
* Like applying the modifier, this changes actual mesh data, not disps
* Some attempt is made to avoid shrinking the base mesh too much, but the algorithm used is just my guess based on how catmull clark behaves
* So far as I know there are no published algorithms for correctly reversing catmull clark when the subdivided mesh has been deformed