Blender Git Loki

Fix T39174 Bevel didn't maintain edge attributes.

When rebuilding the polygons that touch bevel-involved vertices,
need to copy the edge attributes from corresponding original edges.
Special treatment of corner segments, to maintain continuity of
smooth and seam attributes.
Another fix: if have four meeting edges, two opposite ones beveled
and the other two not, propgate the non-beveled-edges attributes
across the line that joins them (perpendicular to the bevel).