child.path to a path relative to tree.model.sort.  That is,
child.path points to a path in the child model.  The returned path will
point to the same row in the sorted model.  If child.path isn't a valid 
path on the child model, then NULL is returned.gtkTreeModelSortConvertChildPathToPath(object, child.path)objectchild.pathGtkTreePath to convertGtkTreePath] A newly allocated GtkTreePath, or NULL