product: raise an exception if the dict are different

Fixes #132.

* python/spot.py (translate): Allow changing the dictionary.
* tests/python/prodexpt.py: New file.
* tests/Makefile.am: Add it.
* spot/twa/twaproduct.cc, spot/twaalgos/product.cc: Add them.
* NEWS: Mention the change.

tests/python/prodexpt.py

@@ -0,0 +1,38 @@
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2016  Laboratoire de Recherche et Développement
+# de l'Epita
+#
+# This file is part of Spot, a model checking library.
+#
+# Spot is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# Spot is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+# License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import spot
+
+# make sure that we are not allowed to build the product of two automata with
+# different dictionnaries.
+
+aut1 = spot.translate('Xa')
+aut2 = spot.translate('Xb', dict=spot.make_bdd_dict())
+
+try:
+    spot.product(aut1, aut2)
+    exit(2)
+except RuntimeError:
+    pass
+
+try:
+    spot.otf_product(aut1, aut2)
+    exit(2)
+except RuntimeError:
+    pass