stutter check: cleanup and add test cases

* src/ltltest/ltlfilt.test: Add more tests.
* src/ltltest/stutter.test: New test.
* src/ltltest/Makefile.am: Adjust.
* src/bin/ltlfilt.cc: Catch std::runtime_error.
* src/tgba/tgbasl.hh (make_tgbasl): New function.
* src/tgba/tgbagraph.hh (make_tgba_graph): Add another overload.
* src/tgbaalgos/stutter_invariance.cc,
src/tgbaalgos/stutter_invariance.hh: Take the algorithm version as an
optional integer, and call getenv() only once.
* bench/stutter/stutter_invariance_randomgraph.cc,
bench/stutter/stutter_invariance_formulas.cc: Simplify using the
above functions.

src/ltltest/stutter.test

@@ -0,0 +1,47 @@
+#! /bin/sh
+# -*- coding: utf-8 -*-
+# Copyright (C) 2013, 2014 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/>.
+
+
+# Check for the stutter-invariant formula detection
+. ./defs || exit 1
+
+set -e
+
+randltl=../../bin/randltl
+ltlfilt=../../bin/ltlfilt
+
+FILE=formulae
+rm -f $FILE
+for i in 10 12 14 16 18 20; do
+  $randltl --seed 0   --tree-size $i a b c       -n 100 >> $FILE
+  $randltl --seed 100 --tree-size $i a b c d e f -n 100 >> $FILE
+done
+
+# We do not check i=0, it is too slow.
+for i in 1 2 3 4 5 6 7 8; do
+    SPOT_STUTTER_CHECK=$i
+    export SPOT_STUTTER_CHECK
+    time $ltlfilt --stutter-invariant -F $FILE > res.$i
+done
+
+# All results should be equal
+for i in 2 3 4 5 6 7 8; do
+    diff res.1 res.$i
+done