Fixes#267
* spot/twaalgos/gfguarantee.cc: Fix a typo when comparing automata
sizes.
* spot/twaalgos/translate.cc, spot/twaalgos/translate.hh: Use
ltl-split even for BA/TGBA, but only of conjunctions with GF(..)
in those cases.
* tests/core/ltl2tgba2.test: Adjust and add the example of #267.
* tests/core/degenid.test, tests/core/parity2.test,
tests/core/stutter-tgba.test, tests/python/automata.ipynb,
tests/python/highlighting.ipynb, tests/python/stutter-inv.ipynb,
bin/spot-x.cc: Adjust.
Fixes#282.
* spot/misc/bddlt.hh (bdd_less_than_stable): New function.
* spot/twa/twagraph.cc (merge_edges): Use it.
* tests/core/genltl.test: Adjust, and add an extra test
for the behavior of #282.
* tests/core/complement.test, tests/core/degenid.test,
tests/core/ltldo.test, tests/core/prodor.test,
tests/core/readsave.test, tests/core/sbacc.test,
tests/python/atva16-fig2a.ipynb, tests/python/automata.ipynb,
tests/python/decompose.ipynb, tests/python/dualize.py,
tests/python/highlighting.ipynb, tests/python/piperead.ipynb,
tests/python/product.ipynb, tests/python/simstate.py,
tests/python/tra2tba.py: Adjust all expected outputs.
* NEWS: Mention the bug.
