reordering GtkListStore items

[Paul Pogonyshev <pogonyshev gmx net>]

Is there an easy way to swap a given list store item with
next/previous item?  I'm facing two problems: there appear
to be no reordering functions in GTK+ 2.0 (all marked as
"since 2.2") and there is gtk_tree_model_iter_next(), but
no gtk_tree_mode_iter_previous().

In other words: can I implement "Move up" / "Move down"
buttons without much pain?

Paul