This avoids a small regression on the size of degeneralized
automata of our usual list of literature formulae.

* src/tgba/tgbatba.hh, src/tgba/tgbatba.cc
(tgba_tba_proxy::union_acceptance_conditions_of_original_state):
New method.
* src/tgba/tgbatba.cc (tgba_tba_proxy_succ_iterator): In accepting
states, ignore only the last expected acceptance condition if its
common to all outgoing transitions AND if it is not used by any
outgoing transitions of the destination.