fix a memory leak in basic LTL simplifications

When something like XFa & FXa is reduced, the subformulae XFa and FXa
are both rewritten separately to XFa, and then the vector of arguments
of the And operators, [XFa,XFa], is passed through a specialized loop
that searches of the form X(...) that can potentially be simplified with
some other terms.  This loop converts the vector [XFa,XFa] into the set
{XFa,XFa}={XFa} and forgot to deal with the case where the insertion
would actually not add an existing subformula.

* src/ltlvisit/simplify.cc: Fix the code for Or, and And.
* src/ltltest/reduc0.test: New file, to test it.
* src/ltltest/Makefile.am (TESTS): Add it.
* src/ltltest/reduccmp.test: Add an extra test that does not
trigger the bug (because reduccmp.test uses more than basic
optimizations, and the implication-based simplifications are
already able to detect that XFa and FXa are equivalent).

src/ltltest/Makefile.am

@@ -95,6 +95,7 @@ TESTS = \
   isop.test \
   syntimpl.test \
   reduc.test \
+  reduc0.test \
   reducpsl.test \
   reduccmp.test \
   uwrm.test

src/ltltest/reduc0.test

@@ -0,0 +1,26 @@
+#! /bin/sh
+# Copyright (C) 2013 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 || exit 1
+set -e
+
+# These two reductions used to cause a memory leak.
+run 0 ../reduc 0 'XFa & FXa' 'XFa'
+run 0 ../reduc 0 '(Xf W 0) | X(f W 0)' 'XGf'
+

src/ltltest/reduccmp.test

@@ -99,6 +99,9 @@ for x in ../reduccmp ../reductaustr; do
      run 0 $x 'FX(a)' 'XF(a)'
      run 0 $x 'GX(a)' 'XG(a)'
 
+     run 0 $x '(Xf W 0) | X(f W 0)' 'XGf'
+     run 0 $x 'XFa & FXa' 'XFa'
+
      run 0 $x 'GF(a | Xb)' 'GF(a | b)'
      run 0 $x 'GF(a | Fb)' 'GF(a | b)'
      run 0 $x 'GF(Xa | Fb)' 'GF(a | b)'