Quadriflow does not support non manifold meshes. (Edges with > 3
connected faces and discontinuous face normal directions)
While it does sometimes "work" in these configurations, the results are
not good and in most cases it just flat out will crash.
Added a sanity check to make sure that the input mesh is manifold.
Reviewed By: Brecht
Differential Revision: http://developer.blender.org/D5877
f025b625f4