* NEWS: Document this.
* spot/twa/twagraph.cc: `copy_state_names_from` handles this new info.
* spot/twaalgos/degen.hh, spot/twaalgos/degen.cc: Implement it.
* tests/python/origstate.py, tests/python/simstate.py: Update tests to
reflect the change.
* spot/twa/twagraph.cc, spot/twa/twagraph.hh: Here. Also
make sure "original-states" survives defrag_states().
* NEWS: Mention it.
* tests/python/origstate.py: New file.
* tests/Makefile.am: Add it.