twa_graph: introduce copy_state_names_from()

* spot/twa/twagraph.cc, spot/twa/twagraph.hh: Here.  Also
make sure "original-states" survives defrag_states().
* NEWS: Mention it.
* tests/python/origstate.py: New file.
* tests/Makefile.am: Add it.

tests/Makefile.am

@@ -346,6 +346,7 @@ TESTS_python = \
   python/minato.py \
   python/misc-ec.py \
   python/optionmap.py \
+  python/origstate.py \
   python/otfcrash.py \
   python/parsetgba.py \
   python/prodexpt.py \

tests/python/origstate.py

@@ -0,0 +1,108 @@
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2015, 2017  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
+from sys import exit
+
+aut = spot.automaton("""
+HOA: v1
+States: 2
+Start: 0
+AP: 2 "a" "b"
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+--BODY--
+State: 0
+[0] 0 {0}
+[!0] 0
+[1] 1
+State: 1
+[1] 1 {0}
+--END--
+""")
+
+aut2 = spot.degeneralize(aut)
+assert aut2.to_str() == """HOA: v1
+States: 3
+Start: 0
+AP: 2 "a" "b"
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+properties: trans-labels explicit-labels state-acc
+--BODY--
+State: 0 {0}
+[0] 0
+[!0] 1
+[1] 2
+State: 1
+[0] 0
+[!0] 1
+[1] 2
+State: 2 {0}
+[1] 2
+--END--"""
+
+aut2.copy_state_names_from(aut)
+assert aut2.to_str() == """HOA: v1
+States: 3
+Start: 0
+AP: 2 "a" "b"
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+properties: trans-labels explicit-labels state-acc
+--BODY--
+State: 0 "0" {0}
+[0] 0
+[!0] 1
+[1] 2
+State: 1 "0"
+[0] 0
+[!0] 1
+[1] 2
+State: 2 "1" {0}
+[1] 2
+--END--"""
+
+aut2.set_init_state(2)
+aut2.purge_unreachable_states()
+ref = """HOA: v1
+States: 1
+Start: 0
+AP: 2 "a" "b"
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+properties: trans-labels explicit-labels state-acc colored
+properties: deterministic
+--BODY--
+State: 0 "1" {0}
+[1] 0
+--END--"""
+assert aut2.to_str() == ref
+# This makes sure that the original-states vector has also been renamed.
+aut2.copy_state_names_from(aut)
+assert aut2.to_str() == ref
+
+aut2 = spot.degeneralize(aut)
+aut2.release_named_properties()
+try:
+    aut2.copy_state_names_from(aut)
+except RuntimeError as e:
+    assert "state does not exist in source automaton" in str(e)
+else:
+    exit(1)