pcm_convert: make C++ safe

src/pcm_convert.h

 /*
- * Copyright (C) 2003-2011 The Music Player Daemon Project
+ * Copyright (C) 2003-2013 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -25,6 +25,8 @@
 #include "pcm_dither.h"
 #include "pcm_buffer.h"
 
+#include <glib.h>
+
 struct audio_format;
 
 /**
@@ -52,6 +54,8 @@ pcm_convert_quark(void)
 	return g_quark_from_static_string("pcm_convert");
 }
 
+G_BEGIN_DECLS
+
 /**
  * Initializes a pcm_convert_state object.
  */
@@ -91,4 +95,6 @@ pcm_convert(struct pcm_convert_state *state,
 	    size_t *dest_size_r,
 	    GError **error_r);
 
+G_END_DECLS
+
 #endif