These are meant to test the optimization implemented in issue #568.

* spot/gen/automata.hh, spot/gen/automata.cc, bin/genaut.cc: Add
support for --cycle-log-nba and --cycle-onehot-nba.
* tests/core/genaut.test: Add some tests.
* tests/python/gen.ipynb: Illustrate them.
* NEWS: Mention them.