ltlfilt, genltl: factor the common output options.

* src/bin/common_output.cc, src/bin/common_output.hh: New file
with the common output code.
* src/bin/Makefile.am: Add them.
* src/bin/genltl.cc, src/bin/ltlfilt.cc: Simplify, using
argp's children parser, and calling output_formula().

src/bin/common_output.hh

@@ -0,0 +1,41 @@
+// -*- 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_BIN_COMMON_OUTPUT_HH
+#define SPOT_BIN_COMMON_OUTPUT_HH
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <argp.h>
+#include "ltlvisit/tostring.hh"
+
+enum output_format_t { spot_output, spin_output, utf8_output };
+extern output_format_t output_format;
+extern bool full_parenth;
+
+extern const struct argp output_argp;
+
+int parse_opt_output(int key, char* arg, struct argp_state* state);
+void output_formula(const spot::ltl::formula* f);
+
+#endif // SPOT_BIN_COMMON_OUTPUT_HH