mrdoob/three.js — pull request #5323 by Wilt (2014-09-16 20:07:16+00:00)
Title: Add invert method to invert the face Vertex order

Sometimes the face vertex order is not counterclockwise resulting in the material to render on the backside of the face. To quickly solve this issue it would be useful to have an invert method in THREE.Face3. Hope you also see the use of such a method.