Implement Loizou & Thanisch's algorithm for enumerating cycles.

* src/tgbaalgos/cycles.cc, src/tgbaalgos/cycles.hh,
src/tgbatest/cycles.test: New files.
* src/tgbaalgos/Makefile.am, src/tgbatest/Makefile.am: Add them.
* src/tgbatest/ltl2tgba.cc: Add a -KC option for testing.

src/tgbatest/cycles.test

@@ -0,0 +1,62 @@
+#!/bin/sh
+# Copyright (C) 2012 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 2 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 Spot; see the file COPYING.  If not, write to the Free
+# Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+# 02111-1307, USA.
+
+# While running some benchmark, Tomáš Babiak found that Spot took too
+# much time (i.e. >1h) to translate those six formulae.  It turns out
+# that the WDBA minimization was performed after the degeneralization
+# algorithm, while this is not necessary (WDBA will produce a BA, so
+# we may as well skip degeneralization).  Translating these formulae
+# in the test-suite ensure that they don't take too much time (the
+# buildfarm will timeout if it does).
+
+. ./defs
+
+set -e
+
+# Fig.1 from Johnson's SIAM J. Comput. 1975 paper.
+
+(
+echo 'acc = ;'
+k=3
+v=`expr $k + 2`
+w=`expr 2 \* $k + 2`
+x=`expr 3 \* $k + 3`
+for i in $(seq 2 `expr $k + 1`); do
+  echo "s1,s$i,,;"
+  echo "s$i,s$v,,;"
+done
+for i in $(seq `expr $k + 2` `expr 2 \* $k`); do
+  echo "s$i,s`expr $i + 1`,,;"
+  echo "s$i,s$w,,;"
+done
+echo "s`expr 2 \* $k + 1`,s$w,,;"
+echo "s`expr 2 \* $k + 1`,s1,,;"
+for i in $(seq `expr 2 \* $k + 3` `expr 3 \* $k + 2`); do
+  echo "s$w,s$i,,;"
+  echo "s$i,s$x,,;"
+done
+echo "s`expr 2 \* $k + 3`,s$v,,;"
+echo "s$x,s$w,,;"
+) > johnson-fig1.tgba
+
+
+run 0 ../ltl2tgba -KC -X johnson-fig1.tgba > out
+test `wc -l < out` -eq 10