scc_info: fix split_on_sets

* spot/twaalgos/sccinfo.cc (split_on_sets): Correctly register APs.
* tests/python/sccsplit.py: New file.
* tests/Makefile.am: Add it.
* NEWS: Mention the bug.

tests/python/sccsplit.py

@@ -0,0 +1,30 @@
+#!/usr/bin/python3
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2018 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
+
+aut = spot.translate('GF(a <-> Xa) & GF(b <-> XXb)')
+si = spot.scc_info(aut)
+s = ""
+for aut2 in si.split_on_sets(0, [0]):
+    # This call to to_str() used to fail because split_on_sets had not
+    # registered the atomic propositions of aut
+    s += aut2.to_str();
+assert spot.automaton(s).num_states() == 8