Add an LTL printer in LBT's syntax.

* src/ltlvisit/lbt.cc, src/ltlvisit/lbt.hh: New files.
* src/ltlvisit/Makefile.am: Add them.
* src/bin/common_output.cc, src/bin/common_output.hh: Add
support for LBT output, and reporting formulae that cannot
be output in this syntax.
* src/bin/ltlfilt.cc: Pass filename and linenum to
output_formula() for better error reporting.

src/ltlvisit/lbt.hh

@@ -0,0 +1,51 @@
+// -*- coding: utf-8 -*-
+// 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.
+
+#ifndef SPOT_LTLVISIT_LBT_HH
+# define SPOT_LTLVISIT_LBT_HH
+
+#include <ltlast/formula.hh>
+#include <iosfwd>
+
+namespace spot
+{
+  namespace ltl
+  {
+    /// \addtogroup ltl_io
+    /// @{
+
+    /// \brief Output an LTL formula as a string in LBT's format.
+    ///
+    /// The formula must be an LTL formula (ELTL and PSL operators
+    /// are not supported).  The M and W operator will be output
+    /// as-is, because this is accepted by LBTT, however if you
+    /// plan to use the output with other tools, you should probably
+    /// rewrite these two operators using unabbreviate_wm().
+    ///
+    /// \param f The formula to translate.
+    /// \param os The stream where it should be output.
+    std::ostream&
+    to_lbt_string(const formula* f, std::ostream& os);
+    /// @}
+  }
+}
+
+#endif // SPOT_LTLVISIT_TOSTRING_HH