2.5 Armature Editing - Restored 'Align Bones' (Ctrl Alt A)

2.5 Armature Editing - Restored 'Align Bones' (Ctrl Alt A)

* I've had to remap 'Duplicate window' to Ctrl Alt W instead...

* Fixed some bugs with armature context iterators for X-Axis Mirroring. Now, the code there checks for mirrored bones in the right way.
For details on how to write tools that need to cope with this option, refer to the 'Align Bones' operator. I'll port another simple operator as another good example soon.

Additional notes:
Currently, armature_sync_selection() is really buggy (not part of this commit), and needs further attention.