[blender] Don't hide KeyError in various calling_action

While here, instead of triggering some exception at each iteration of
blender main loop, just exit properly with a backtrace.
[armature] Fix a bug hidden by the KeyError massive exception handling
Fixed two major bugs in armatures

- in Armature: head_pose -> pose_head
- in ArmaturePose: default action ignored some joints
[pr2] Fixed the rotation direction of some of the armature joints

Done by rotating by 180deg the 'roll' value of the individual bones (in Edit mode)