fix position changes when sitting on a prim with position and/or orientation explicitly specified
Only translate linked prim specified offset pos by the link prim rotation, not any specified avatar rotation as well.

Don't translate root prim position by avatar rotation.
Fix stand positions rather than having the stand jump to the root prim.
Restore SP.AbsolutePosition to properly return actual absolute position when sitting
Fix regression where sitting on ground stopped working.

This was due to the PhysicsActor no longer being recreated on stand from ground.
Merge branch 'link-sitting'