Blender Git Loki

Fix mesh shrinking when using the relax mesh filter.

If the relax mesh filter was used on a non manifold mesh with open
boundaries, all the vertices were relaxed and the mesh was shrinking.
This was an unintended behavior that was making the filter unusable with
these meshes.

The mesh filter is now initializing an automasking buffer using the same
boundary automasking function from the brush code. Now edges are
preserved and the relax filter works as it should.

Reviewed By: jbakker

Differential Revision: https://developer.blender.org/D7097