Blender Git Loki

Partially replace convex hull implementation with Bullet implementation

* Bullet's convex hull implementation is significantly more robust
than the one I implemented, as well as being faster.

* This fixes bug [#32864] "Convex Hull fails in some cases."
projects.blender.org/tracker/?func=detail&aid=32864&group_id=9&atid=498

That bug, and others like it, relate to the poor handling of
co-planar surfaces in the input. Pretty much any model that is
simple-subdivided a few times gave very bad results before, Bullet's
implementation handles this much better.

* In order to ensure a smooth transition, the Bullet output is
translated into the existing HullTriangle hash structure. This makes
it easy to ensure that the existing slot output stays the same; the
interactions between the slots are somewhat complicated, detangling
is a TODO.

* Reviewed by Brecht:
https://codereview.appspot.com/6741063