Always rescan and update playlists

This is needed to keep relative playlist items up to date in the
database when the playlist file moves around.

src/db.h

@@ -273,6 +273,9 @@ db_pl_add(char *title, char *path, int *id);
 int
 db_pl_add_item(int plid, int mfid);
 
+void
+db_pl_clear_items(int id);
+
 void
 db_pl_delete(int id);