simplify_acceptance: fix handling of first edge

Fixes #315.

* spot/twaalgos/cleanacc.cc (simplify_acceptance_here): Do not
compare the first edge against previous_a.
* tests/core/accsimpl.test: New file.
* tests/Makefile.am: Add it.
* NEWS: Mention the bug.

tests/Makefile.am

@@ -242,6 +242,7 @@ TESTS_twa = \
   core/explpro4.test \
   core/explsum.test \
   core/dualize.test \
+  core/accsimpl.test \
   core/tripprod.test \
   core/dupexp.test \
   core/exclusive-tgba.test \

tests/core/accsimpl.test

@@ -0,0 +1,30 @@
+#!/bin/sh
+# -*- coding: utf-8 -*-
+# Copyright (C) 2018 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/>.
+
+
+. ./defs
+
+set -e
+
+
+# Issue #315
+ltlcross -f FGa \
+  'ltl2tgba -G -D %f | autfilt --complement >%O' \
+  'ltl2tgba -G -D %f | autfilt --complement | autfilt --simplify-acceptance >%O'