python: add wrapper for libspotgen

For #254.

* python/spot/gen.i, tests/python/gen.py: New files.
* python/Makefile.am, tests/Makefile.am: Adjust.
* NEWS: Mention the spot.gen python package.

tests/Makefile.am

@@ -335,6 +335,7 @@ TESTS_python = \
   python/declenv.py \
   python/decompose_scc.py \
   python/dualize.py \
+  python/gen.py \
   python/implies.py \
   python/interdep.py \
   python/ltl2tgba.test \

tests/python/gen.py

@@ -0,0 +1,38 @@
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2017 Laboratoire de Recherche et Développement de
+# l'Epita (LRDE).
+#
+# 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/>.
+
+# Test that the spot.gen package works, in particular, we want
+# to make sure that the objects created from spot.gen methods
+# are usable with methods from the spot package.
+
+import spot.gen as gen
+from sys import exit
+
+k2 = gen.ks_cobuchi(2)
+assert k2.num_states() == 5
+# to_str is defined in the spot package, so this makes sure
+# the type returned by spot.gen.ks_cobuchi() is the correct one.
+assert 'to_str' in dir(k2)
+
+try:
+    gen.ks_cobuchi(0)
+except RuntimeError as e:
+    assert 'positive argument' in str(e)
+else:
+    exit(2)