decoder_api.h, ...: add "extern C"

test/DumpDatabase.cxx

@@ -24,11 +24,8 @@
 #include "Directory.hxx"
 #include "song.h"
 #include "PlaylistVector.hxx"
-
-extern "C" {
 #include "conf.h"
 #include "tag.h"
-}
 
 #include <iostream>
 using std::cout;

test/dump_playlist.cxx

@@ -21,13 +21,13 @@
 #include "TagSave.hxx"
 #include "song.h"
 #include "Directory.hxx"
+#include "input_stream.h"
+#include "conf.h"
+#include "decoder_api.h"
 
 extern "C" {
 #include "io_thread.h"
 #include "input_init.h"
-#include "input_stream.h"
-#include "conf.h"
-#include "decoder_api.h"
 #include "decoder_list.h"
 #include "playlist_list.h"
 #include "playlist_plugin.h"

test/run_input.cxx

@@ -20,13 +20,13 @@
 #include "config.h"
 #include "TagSave.hxx"
 #include "stdbin.h"
+#include "tag.h"
+#include "conf.h"
+#include "input_stream.h"
 
 extern "C" {
 #include "io_thread.h"
 #include "input_init.h"
-#include "input_stream.h"
-#include "tag.h"
-#include "conf.h"
 
 #ifdef ENABLE_ARCHIVE
 #include "archive_list.h"

test/run_output.cxx

@@ -19,12 +19,12 @@
 
 #include "config.h"
 #include "OutputControl.hxx"
+#include "conf.h"
 
 extern "C" {
 #include "output_plugin.h"
 #include "output_internal.h"
 #include "io_thread.h"
-#include "conf.h"
 #include "audio_parser.h"
 #include "filter_registry.h"
 #include "pcm_convert.h"