Since b[+] and [*0] are siSERE, b* is siSERE as well.
Suggested by Victor Khomenko.
* spot/tl/formula.cc: Implement that for Star and also
in the concatenation rule.
* tests/core/kind.test, tests/core/ltlfilt.test: Adjust.
Reported by Victor Khomenko.
* spot/tl/formula.cc: Rewrite the siPSL detection for ";".
* tests/core/ltlfilt.test: Add more tests.
* tests/core/kind.test: Adjust.
* NEWS: Mention the bug.