ltl2tgba: clear simplification cache between translations
The cache used in formula simplification will keep atomic propositions defined between several translations, and may impact variable order. Reported by Maximilien Colange. * spot/tl/simplify.hh, spot/tl/simplify.cc, spot/twaalgos/translate.cc, spot/twaalgos/translate.hh (clear_cache): New method. * bin/ltl2tgba.cc, bin/ltl2tgta.cc: Call it. * spot/twaalgos/stats.cc: Do not keep a point to the formula after printing statistics. * tests/core/ltl2tgba.test: Add a test case. * tests/core/readsave.test: Adjust one formula. * NEWS: Mention the issue.