speed-up dyn-topo by storing the edge-loops rather then edge-faces.
- no need for bm_triangle_other_vert_find(), the other vert is known relative to the loop.
- no need for bm_face_edge_backwards(), the verts are in order in the loop.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53859 954f8c5b-7b00-dc11-b283-0030488c597c