Suggested by Nikos Gorogiannis.

* src/tgba/tgbatba.hh (tgba_tba_proxy::create_state): New method.
(tgba_tba_proxy::uniq_map_): New attribute.
* src/tgba/tgbatba.cc (state_tba_proxy): Use the default
copy constructor.  Empty the destructor.  Implement an empty
destroy() method.  Use addresses for comparison.  Make clone()
a no-op.
(tgba_tba_proxy): Allocate and deallocate the unicity table.
Implement create_sates().
(tgba_tba_proxy, tgba_sba_proxy, tgba_tba_proxy_succ_iterator):
Adjust state construction to call create_state().