* NEWS: mention this fix.
* bench/stutter/stutter_bench.sh, bench/stutter/user.sh: Path to spot
binaries would include an inexistant src directory.
* bench/stutter/stutter_invariance_formulas.cc: Add override qualifier
to satisfy -Wsuggest-override.
* src/tgbaalgos/stutter.cc: Add a new variant of Etessami's check,
closer to his original paper in IPL.
* src/ltltest/stutter.test: Add more tests.
* bench/stutter/user.sh: Include this new variant in the benchmark.