This allows fixing issue #388 reported by Victor Khomenko.

* spot/twaalgos/word.cc, spot/twaalgos/word.hh (use_all_aps): New
method.
* tests/python/stutter-inv.ipynb: Use it.
* tests/python/stutter.py: New file, with Victor's test case.
* tests/Makefile.am: Add python/stutter.py.