trival: new class for tri-valued logic

* spot/misc/trival.hh: New file.
* spot/misc/Makefile.am: Add it.
* python/spot_impl.i: Add Python bindings.
* tests/core/trival.cc, tests/core/trival.test,
tests/python/trival.py: New files, testing it.
* tests/Makefile.am: Add them.

tests/python/trival.py

@@ -0,0 +1,42 @@
+# -*- 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
+
+v1 = spot.trival()
+v2 = spot.trival(False)
+v3 = spot.trival(True)
+v4 = spot.trival_maybe()
+assert v1 != v2
+assert v1 != v3
+assert v2 != v3
+assert v4 != v2
+assert v4 != v3
+assert v2 == False
+assert True == v3
+assert v4 == spot.trival_maybe()
+assert v3
+assert -v2
+assert not -v1
+assert not v1;
+assert not -v3
+
+for u in (v1, v2, v3):
+  for v in (v1, v2, v3):
+      assert (u & v) == -(-u | -v)