Reorganize this function so that syntactically there is only one
loop over the successors, and not two. Call reintroduce the call
to couvreur99_check_shy::state_index(), needed by SSP, and
suppress that to index_and_insert introduced on 2004-12-29. Also
split the "group" option in two: "group" and "group2". "group2"
is the equivalent of the older "group", while the new "group" is
weaker and faster.
(couvreur99_check_shy::state_index): Change prototype as needed by
the algorithm.
* src/tgbaalgos/gtec/gtec.hh: Adjust.
* src/tgbaalgos/gtec/nsheap.hh, src/tgbaalgos/gtec/nsheap.cc
(index_and_insert): Remove.
* iface/gspn/ssp.cc (couvreur99_check_shy_ssp::state_index): Adjust
to new prototype.
* bench/emptchk/README, bench/emptchk/algorithms: Adjust references
to group/group2.