Speedup tgba_product when one of the argument is a Kripke structure.
The gain is not very impressive. The runtime of the first example in iface/dve2/README (also in dve2check.test) is 15% faster. * src/tgba/tgbaproduct.hh (tgba_succ_iterator_product): Move ... * src/tgba/tgbaproduct.cc (tgba_succ_iterator_product, tgba_succ_iterator_product_common): ... in these two classes. (tgba_succ_iterator_product_kripke): New class to speedup successor computation on Kripke structures. We can assume that all the transitions leaving the same state have the same label. (tgba_product::tgba_product, tgba_product::succ_iter): Use tgba_succ_iterator_product_kripke when appropriate. (tgba_product_init::tgba_product_init): Adjust for the case where tgba_product did reverse its operands.