New keyword parameters for Mesh.faces.extend() method:
* ignoreDups: turns off checks for duplicate faces in the input list and
existing mesh faces. Intended for constructing new meshes where the
faces are known to be unique.
* indexList: makes the method return a list of new faces indices, which
can be used to index new faces to add other attributes like color. If
duplicate faces are removed, None is placed in their list slot.