From BlenderWiki
Pose Bone RotScale Parenting
Note: basic page, will enhance it asap!
This patch replaces the Hinge/No Scale options of bones by the ability to choose any bone upper in the chain as rotation/scale reference.
So choosing the immediate parent is usual behavior, choosing none is old Hinge and/or No Scale, and choosing another bone… is new option!
On a code level, it adds two new rot_parent and scale_parent bones pointers to each bone, and adapt the pose bone evaluation code, as well as many editing code (to check/avoid invalid situations when adding/reparenting/removing/etc. bones in EditMode).
Coded from an idea of Bassam Kurdali (which did first tests of this patch on a user POV). Patch not yet definitive, have a few additional suggestions to implement.
