python: improve kripke_graph bindings

Related to issue #376.

* spot/kripke/kripkegraph.hh: Avoid indirect type definitions for the
benefit of Swig.
* python/spot/impl.i: Add bindings for iterators over kripke_graph
states and edges.
* tests/python/kripke.py: New file.
* tests/Makefile.am: Add it.
* NEWS: Update.

tests/python/kripke.py

@@ -0,0 +1,75 @@
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2019 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/>.
+
+import spot
+import buddy
+bdict = spot.make_bdd_dict()
+k = spot.make_kripke_graph(bdict)
+p1 = buddy.bdd_ithvar(k.register_ap("p1"))
+p2 = buddy.bdd_ithvar(k.register_ap("p2"))
+cond1 = p1 & p2
+cond2 = p1 & -p2
+cond3 = -p1 & -p2
+s2 = k.new_state(cond1)
+s1 = k.new_state(cond2)
+s3 = k.new_state(cond3)
+k.new_edge(s1, s2)
+k.new_edge(s2, s2)
+k.new_edge(s1, s3)
+k.new_edge(s3, s3)
+k.new_edge(s3, s2)
+k.set_init_state(s1)
+
+hoa="""HOA: v1
+States: 3
+Start: 0
+AP: 2 "p1" "p2"
+acc-name: all
+Acceptance: 0 t
+properties: state-labels explicit-labels state-acc
+--BODY--
+State: [0&!1] 0 "1"
+1 2
+State: [0&1] 1 "0"
+1
+State: [!0&!1] 2 "2"
+2 1
+--END--"""
+assert hoa == k.to_str('HOA')
+assert k.num_states() == 3
+assert k.num_edges() == 5
+
+res = []
+for e in k.out(s1):
+    res.append((e.src, e.dst))
+assert res == [(1, 0), (1, 2)]
+
+res = []
+for e in k.edges():
+    res.append((e.src, e.dst))
+assert res == [(1, 0), (0, 0), (1, 2), (2, 2), (2, 0)]
+
+res = []
+for s in k.states():
+    res.append(s.cond())
+assert res == [cond1, cond2, cond3]
+
+assert k.states()[0].cond() == cond1
+assert k.states()[1].cond() == cond2
+assert k.states()[2].cond() == cond3