remprop: reset no-terminal property

Reported by Yong Li.

* spot/twaalgos/remprop.cc: Here.
* tests/python/removeap.py: New test case.
* tests/Makefile.am: Add it.
* NEWS: Document the issue.
* THANKS: Add Yong Li.

tests/python/removeap.py

@@ -0,0 +1,33 @@
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2019  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('a U (c & Gb)')
+assert not spot.is_terminal_automaton(aut)
+assert aut.prop_terminal().is_false()
+rem = spot.remove_ap()
+rem.add_ap("b")
+aut = rem.strip(aut)
+assert not aut.prop_terminal().is_false()
+assert spot.is_terminal_automaton(aut)
+assert aut.prop_terminal().is_true()
+aut = rem.strip(aut)
+assert aut.prop_terminal().is_true()