We do not remove them in rejecting SCCs (as it might make the SCC
accepting), but we can remove them between SCCs.
Fixes#101.
* src/twaalgos/sccfilter.cc: Here.
* src/tests/sccsimpl.test: Add test case.
* NEWS: Mention this.
* src/twaalgos/sccfilter.cc (acc_filter_some, acc_filter_all): Merge
into...
(acc_filter_mask): ... this single parametrized class, and only
remove sets that are only used as Inf.
* src/twa/acc.hh: Add missing operator~.
* src/tests/sccsimpl.test: Add test case.
* src/tests/sccdot.test: Adjust.
* NEWS: Mention the bug.