Blender Git Loki

As suggested by Campbell, rather use BVHTree to get len_diff in this morning's fix.

Note than it's using nearest faces, since it showed to be much more performant than
nearest vertex (quite odd, it's about 40% slower for the first element, then 50 times quicker
for all others, as if BVH was cached, and building face was slower than verts one,
but then using it, much quicker!).