Revert everything related to Damien's work in 2008 (he will commit a new version soon).

Here are the reverted patches:
8c0d1003b0,
25a3114287,
9afbaf6342,
dc0005f4e1,
543190f2bc.

src/ltlast/visitor.hh

@@ -0,0 +1,74 @@
+// Copyright (C) 2003, 2004, 2005  Laboratoire d'Informatique de Paris 6 (LIP6),
+// département Systèmes Répartis Coopératifs (SRC), Université Pierre
+// et Marie Curie.
+//
+// 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.
+
+/// \file ltlast/visitor.hh
+/// \brief LTL visitor interface
+#ifndef SPOT_LTLAST_VISITOR_HH
+# define SPOT_LTLAST_VISITOR_HH
+
+#include "predecl.hh"
+
+namespace spot
+{
+  namespace ltl
+  {
+    /// \brief Formula visitor that can modify the formula.
+    /// \ingroup ltl_essential
+    ///
+    /// Writing visitors is the prefered way
+    /// to traverse a formula, since it doesn't
+    /// involve any cast.
+    ///
+    /// If you do not need to modify the visited formula, inherit from
+    /// spot::ltl:const_visitor instead.
+    struct visitor
+    {
+      virtual ~visitor() {}
+      virtual void visit(atomic_prop* node) = 0;
+      virtual void visit(constant* node) = 0;
+      virtual void visit(binop* node) = 0;
+      virtual void visit(unop* node) = 0;
+      virtual void visit(multop* node) = 0;
+    };
+
+    /// \brief Formula visitor that cannot modify the formula.
+    ///
+    /// Writing visitors is the prefered way
+    /// to traverse a formula, since it doesn't
+    /// involve any cast.
+    ///
+    /// If you want to modify the visited formula, inherit from
+    /// spot::ltl:visitor instead.
+    struct const_visitor
+    {
+      virtual ~const_visitor() {}
+      virtual void visit(const atomic_prop* node) = 0;
+      virtual void visit(const constant* node) = 0;
+      virtual void visit(const binop* node) = 0;
+      virtual void visit(const unop* node) = 0;
+      virtual void visit(const multop* node) = 0;
+    };
+
+
+  }
+}
+
+#endif // SPOT_LTLAST_VISITOR_HH