lbtt: improve the LBTT output

Provide a way to output automata with state-based acceptance.  Also
print the guards using to_lbt_string() for consistency: as a
consequence, atomic proposition that do not match p[0-9]+ are now
double-quoted.

* src/tgbaalgos/lbtt.hh (lbtt_reachable): Add a sba option.
* src/tgbaalgos/lbtt.cc: Implement it, and use to_lbt_string().
* src/ltlvisit/lbt.cc (is_pnum): Reject 'p' without number.
* src/bin/ltl2tgba.cc: Activate the sba option of --ba was given.
Add an option --lbtt=t to get the old behavior.
* src/bin/man/ltl2tgba.x: Document the LBTT format we use with
some links and examples.
* src/tgbatest/lbttparse.test: More tests.
* src/tgbatest/ltlcross2.test: Add a check with --lbtt --ba.
* NEWS: Update.

src/tgbaalgos/lbtt.hh

@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2012 Laboratoire de Recherche et Développement de
+// Copyright (C) 2012, 2013 Laboratoire de Recherche et Développement de
 // l'Epita (LRDE).
 // Copyright (C) 2003, 2004  Laboratoire d'Informatique de Paris 6 (LIP6),
 // département Systèmes Répartis Coopératifs (SRC), Université Pierre
@@ -29,13 +29,15 @@
 
 namespace spot
 {
-  /// \brief Print reachable states in LBTT format.
+  /// \brief Print reachable states in LBTT's format.
   /// \ingroup tgba_io
   ///
   /// \param g The automata to print.
   /// \param os Where to print.
-  std::ostream& lbtt_reachable(std::ostream& os, const tgba* g);
-
+  /// \param sba Assume \a g is an SBA and use LBTT's state-based
+  /// acceptance format (similar to LBT's format).
+  std::ostream& lbtt_reachable(std::ostream& os, const tgba* g,
+			       bool sba = false);
 
   /// \brief Read an automaton in LBTT's format
   /// \ingroup tgba_io