Simple deform modifier: replace factor property by angle for twist and bend
modes, so we can show degrees rather than radians. Still refers to the same
DNA variable to keep backwards compatibility.

Patch #33807 by Gottfried Hofmann.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55055 954f8c5b-7b00-dc11-b283-0030488c597c