include config.h in all sources

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

src/decoder/_ogg_common.h

@@ -24,7 +24,7 @@
 #ifndef MPD_OGG_COMMON_H
 #define MPD_OGG_COMMON_H
 
-#include "../decoder_api.h"
+#include "decoder_api.h"
 
 typedef enum _ogg_stream_type { VORBIS, FLAC } ogg_stream_type;