playlist_queue: moved check_translate_song() to playlist_song.c

Makefile.am

@@ -156,6 +156,7 @@ mpd_headers = \
 	src/playlist_state.h \
 	src/playlist_plugin.h \
 	src/playlist_list.h \
+	src/playlist_song.h \
 	src/playlist_queue.h \
 	src/playlist/extm3u_playlist_plugin.h \
 	src/playlist/m3u_playlist_plugin.h \
@@ -295,6 +296,7 @@ src_mpd_SOURCES = \
 	src/playlist_edit.c \
 	src/playlist_print.c \
 	src/playlist_save.c \
+	src/playlist_song.c \
 	src/playlist_state.c \
 	src/playlist_queue.c \
 	src/queue.c \