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

warnings.

test/check_sizeof.c

@@ -1,7 +1,5 @@
 /*
-    $Id: check_sizeof.c,v 1.5 2008/03/22 18:08:25 karl Exp $
-
-    Copyright (C) 2001, 2008 Herbert Valerio Riedel <hvr@gnu.org>
+    Copyright (C) 2001, 2008, 2011 Herbert Valerio Riedel <hvr@gnu.org>
 
      This program is free software: you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published by
@@ -19,6 +17,7 @@
 
 #ifdef HAVE_CONFIG_H
 # include "config.h"
+# define __CDIO_CONFIG_H__ 1
 #endif
 
 #include <assert.h>