Blender Git Loki

BMesh: remove unit-length edge-vector cache from normal calculation

Bypass stored edge-vectors for ~16% performance gains.

While this increases unit-length edge-vector calculations by around ~4x
the overhead of a parallel loop over all edges makes it worthwhile.

Note that caching edge-vectors per-vertex performs better and may be
worth investigating further, although in my tests this increases code
complexity with barley measurable benefits over not using cache at all.

Details about performance and possible optimizations are noted in
bm_vert_calc_normals_impl.