Emits the rows-reordered signal on tree_model.
This should be called by models when their rows have been reordered.
a [GtkTreePath-struct|GtkTreePath-struct] pointing to the tree node whose children have been reordered
a valid [GtkTreeIter-struct|GtkTreeIter-struct] pointing to the node whose children have been reordered, or NULL if the depth of path is 0
an array of integers mapping the current position of each child to its old position before the re-ordering, i.e. new_order[newpos] = oldpos