WIP, jason's patch

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56061 954f8c5b-7b00-dc11-b283-0030488c597c
New implementation for twist brushes.

It has much better rotation and avoids the compression effect that old
twist brushes have. Also twisting is now non periodic, meaning you can
twist beyond 180 degrees. The amount of twist is also calculated
relative to the angle formed after first translating the mouse away from
the brush center.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56062 954f8c5b-7b00-dc11-b283-0030488c597c