lbt: Do not write a trailing space.

* NEWS: Mention it.
* src/ltlvisit/lbt.cc: Instead of outputting a space after each
node, output one before each node but the first one.

NEWS

@@ -13,6 +13,8 @@ New in spot 1.0a (not released):
       (instead of binary operators) when placed in double quotes, but
       on output they were output without quotes, making the result
       unparsable.
+    - the to_lbt_string() functions would always output a trailing space.
+      This is not the case anymore.
     - tgba_product::transition_annotation() would segfault when
       called in a product against a Kripke structure.
   * Minor improvements:

src/ltlvisit/lbt.cc

@@ -1,6 +1,6 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2012 Laboratoire de Recherche et
-// Développement de l'Epita (LRDE).
+// Copyright (C) 2012, 2013 Laboratoire de Recherche et Développement
+// de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
 //
@@ -46,12 +46,24 @@ namespace spot
 
       class lbt_visitor: public visitor
       {
+      protected:
+	std::ostream& os_;
+	bool first_;
       public:
+
 	lbt_visitor(std::ostream& os)
-	  : os_(os)
+	  : os_(os), first_(true)
 	{
 	}
 
+	void blank()
+	{
+	  if (first_)
+	    first_ = false;
+	  else
+	    os_ << ' ';
+	}
+
 	virtual
 	~lbt_visitor()
 	{
@@ -60,16 +72,18 @@ namespace spot
 	void
 	visit(const atomic_prop* ap)
 	{
+	  blank();
 	  std::string str = ap->name();
 	  if (!is_pnum(str.c_str()))
-	    os_ << '"' << str << "\" ";
+	    os_ << '"' << str << '"';
 	  else
-	    os_ << str << ' ';
+	    os_ << str;
 	}
 
 	void
 	visit(const constant* c)
 	{
+	  blank();
 	  switch (c->val())
 	    {
 	    case constant::False:
@@ -87,6 +101,7 @@ namespace spot
 	void
 	visit(const binop* bo)
 	{
+	  blank();
 	  switch (bo->op())
 	    {
 	    case binop::Xor:
@@ -129,6 +144,7 @@ namespace spot
 	void
 	visit(const unop* uo)
 	{
+	  blank();
 	  switch (uo->op())
 	    {
 	    case unop::Not:
@@ -182,15 +198,14 @@ namespace spot
 
 	  unsigned n = mo->size();
 	  for (unsigned i = n - 1; i != 0; --i)
-	    os_ << o << ' ';
+	    {
+	      blank();
+	      os_ << o;
+	    }
 
 	  for (unsigned i = 0; i < n; ++i)
-	    {
 	    mo->nth(i)->accept(*this);
 	}
-	}
-      protected:
-	std::ostream& os_;
       };
 
     } // anonymous