Make sure we can multiply two tgba_explicit.

* tgba/state.hh (state::translate, state::clone, state::as_bdd):
New virtual methods.
* tgba/stataebdd.cc (state::translate, state::clone): New methods.
* tgba/stataebdd.hh (state::translate, state::clone): New methods.
* tgba/tgbabddprod.cc (state_bdd_product::clone,
tgba_bdd_product_succ_iterator::~tgba_bdd_product_succ_iterator):
New methods.
(tgba_bdd_product_succ_iterator::first): Reset right_
if any of left_ or right_ is already done (i.e., is empty).
(tgba_bdd_product_succ_iterator::done): Return true
if right_ is NULL.
(tgba_bdd_product_succ_iterator::current_state,
tgba_bdd_product::get_init_state): Work	directory with `state's.
* tgba/tgbabddprod.hh (state_bdd_product::clone,
tgba_bdd_product_succ_iterator::~tgba_bdd_product_succ_iterator):
New methods.
* tgba/tgbabddtranslateproxy.cc
(tgba_bdd_translate_proxy_succ_iterator::
tgba_bdd_translate_proxy_succ_iterator): Work on any kind of iteraator.
(tgba_bdd_translate_proxy_succ_iterator::
~tgba_bdd_translate_proxy_succ_iterator): New method.
(tgba_bdd_translate_proxy_succ_iterator::current_state,
tgba_bdd_translate_proxy::get_init_state,
tgba_bdd_translate_proxy::succ_iter): Work on `state's and
`tgba_succ_iterator's directlry.
(tgba_bdd_translate_proxy::format_state): Delegate formating
to the proxied automata.
* tgba/tgbaexplicit.cc (state_explicit::clone): New method.
* src/tgba/tgbaexplicit.cc (tgba_explicit::get_condition,
tgba_explicit::get_promise): Call ltl::destroy on existing formulae.
* tgbatest/Makefile.am (check_PROGRAMS): Add explprod.
(explprod_SOURCES): New variable.
(TESTS): Add explprod.test.
(CLEANFILES): Add input1 and input2.

src/tgba/tgbaexplicit.hh

@@ -68,6 +68,8 @@ namespace spot
 
     virtual int compare(const spot::state* other) const;
 
+    virtual state_explicit* clone() const;
+
     virtual ~state_explicit()
     {
     }