Make sure config.h or the copy of that gets included only once to reduce duplicate include

warnings.

lib/driver/osx.c

@@ -1,5 +1,6 @@
 /*
-  Copyright (C) 2003, 2004, 2005, 2006, 2008, 2010 Rocky Bernstein <rocky@gnu.org> 
+  Copyright (C) 2003, 2004, 2005, 2006, 2008, 2010, 2011
+   Rocky Bernstein <rocky@gnu.org> 
   from vcdimager code: 
   Copyright (C) 2001 Herbert Valerio Riedel <hvr@gnu.org>
   and VideoLAN code Copyright (C) 1998-2001 VideoLAN
@@ -28,7 +29,8 @@
 */
 
 #ifdef HAVE_CONFIG_H
-#include "config.h"
+# include "config.h"
+# define __CDIO_CONFIG_H__ 1
 #endif
 
 static const char _rcsid[] = "$Id: osx.c,v 1.14 2008/10/17 11:58:52 rocky Exp $";