Insert the new node before node.

def node_insert_before(self, node, new_node):
        """Insert the new node before node."""

        assert(not self.node_is_on_list(new_node))
        assert(node is not new_node)

        prev = self.node_prev(node)
        assert(prev is not None)
        self.node_set_prev(node, new_node)
        self.node_set_next(new_node, node)

        self.node_set_prev(new_node, prev)
        self.node_set_next(prev, new_node)