This separates cloth stiffness and damping forces into tension, compression, and shearing components, allowing more control over the cloth behaviour. This also adds a bending model selector (although the new bending model itself is not implemented in this commit). This is because some of the features implemented here only make sense within the new bending model, while the old model is kept for compatibility. This commit makes non-breaking changes, and thus maintains full compatibility with existing simulations. Reviewed By: brecht Differential Revision: http://developer.blender.org/D3655