Merge transitions in tgba_tba_proxy.
With this change the output of ltl2tgba -f -x -k -DS "GF(p_1) & ... & GF(p_n) uses less than (n+1)^2 transitions when it used exactly (n+1)*(2^n) transitions before. * src/tgba/tgbatba.cc (tgba_tba_proxy_succ_iterator): Merge transitions going to the same states if they are both accepting or if neither are. (state_ptr_bool_t, state_ptr_bool_less_than): Helper type to store a transition in tgba_tba_proxy_succ_iterator. * src/tgba/tgbatba.cc, src/tgba/tgbatba.hh (tgba_tba_proxy::transition_annotation): Remove. We cannot implement this method if transitions are merged.