Blender Git Loki

Refactor 'split faces' mesh code.

Previous version was trying to do a quick and simple process in the case
we were only considering smooth/flat status of faces.

Thing is, even then, the algorithm was not actually working in all
possible situations, e.g. two smooth faces having a single vertex in
common, but no common edges, would not have split that vertex, leading
to incorrect shading etc.

So now, tweaked slightly our split normals code to be able to generate
lnor spaces even when autosmooth is disabled, and we always go that way
when splitting faces.

Using smooth fans from clnor spaces is not only the only way to get 100%
correct results, it also makes face split code simpler.