Rename as ...
(connected_component::set_type): ... this, and define as a hash_set.
(connected_component::has_state): New method.
* src/tgbaalgos/emptinesscheck.cc (connected_component::has_state):
New method.
(emptiness_check::counter_example, emptiness_check::complete_cycle,
emptiness_check::accepting_path): Simplify using has_state().