translate: enable a restricted form of ltl-split for TGBA/BA
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.