* src/tgbaalgos/dotty.cc, src/taalgos/dotty.cc: Honnor the SPOT_DOTEXTRA
environement variable.
* src/tgbatest/readsave.test, wrap/python/tests/automata.ipynb: Test it.
* NEWS, src/bin/man/spot-x.x: Document it.
* wrap/python/spot.py: Introduce spot.translate (and
spot.formula.translate) as well, as a wrapper around the
spot.translator class. Also implement spot.tgba.show()
to allow passing argument to dotty_reachable() before
the result is converted to SVG.
* wrap/python/tests/automata.ipynb: New test file.
* wrap/python/tests/Makefile.am: Add it.