added missing explicit config.h includes

src/decoder/mp4_plugin.c

@@ -1,7 +1,7 @@
 /* the Music Player Daemon (MPD)
  * Copyright (C) 2003-2007 by Warren Dukes (warren.dukes@gmail.com)
  * This project's homepage is: http://www.musicpd.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
  * the Free Software Foundation; either version 2 of the License, or
@@ -17,6 +17,7 @@
  */
 
 #include "../decoder_api.h"
+#include "config.h"
 
 #include "mp4ff.h"