* The symmetrize operation makes the input mesh elements symmetrical,
but unlike mirroring it only copies in one direction. The edges and
faces that cross the plane of symmetry are split as needed to
enforce symmetry.
* The symmetrize operator can be controlled with the "direction"
property, which combines the choices of symmetry plane and
positive-negative/negative-positive. The enum for this is
BMO_SymmDirection.
* Added menu items in the top-level Mesh menu and the WKEY specials
menu.
* Documentation:
http://wiki.blender.org/index.php/User:Nicholasbishop/Symmetrize
* Reviewed by Brecht:
https://codereview.appspot.com/6618059
1de76baf88