A useless acceptance conditions is one that is always implied by
another.

* src/misc/bddop.hh, src/misc/bddop.cc
(compute_neg_acceptance_conditions): New function.
* src/tgba/tgbaexplicit.hh, src/tgba/tgbaexplicit.cc
(set_acceptance_conditions): New function.
* src/tgbaalgos/scc.cc (build_map, build_scc_stats, dump_scc_dot):
Keep track of useful acceptance conditions.
(useful_acc_of): New function.
* src/tgbaalgos/scc.hh (scc_stats, scc_map::scc::useful_scc): New
attributes.
* src/tgbaalgos/sccfilter.cc (filter_iter): Adjust to filter
useless acceptance conditions.
(scc_filter): Compute useful acceptance conditions and pass them
to filter_iter.