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.