Blender Git Loki

Spline IK: support using both original scaling and volume preservation.

Add a new option that makes the Spline IK solver apply volume
preservation on top of the original scaling, considering the
pre-IK scale of the bone as the goal volume to be preserved.

This basically works similar to the Stretch To constraint, and
allows easily rigging a stretchy chain that uniformly follows
its parent's scaling.

Since the Stretch To behavior is more familiar, the new option
is on by default for newly created Spline IK constraints.