This gets rid of many state*/int conversions.  We now use scc_info
instead of scc_map.  Finally the loops are now all 0-based.

* src/tgbaalgos/sccinfo.cc, src/tgbaalgos/sccinfo.hh (weak_sccs): New
method.
* src/tgbaalgos/dtbasat.cc, src/tgbaalgos/dtbasat.hh,
src/tgbaalgos/dtgbasat.cc, src/tgbaalgos/dtgbasat.hh: Use the
tgba_digraph interface.
* src/tgbatest/ltl2tgba.cc: Adjust calls.