* src/tgba/tgbaexplicit.hh (explicit_graph, tgba_explicit): Make the
transition type explicit.
(state_explicit_string::get_iterator): New method.
(explicit_graph::get_transition): Use it.
(tba): Rename as ...
(sba): ... this.
* wrap/python/spot.i: Instanciate explicit_graph and tgba_explicit
for all three types.