insert a node

    Node *node;

	node = initialise_node();


	node->data = data;
	node->prev = nodeB->prev;
    node->next = nodeB;

    if(prevN)
        nodeB->prev->next = node;
    else {
        if(list->head) {
            list->head->prev = node;
        }
        list->head = node;
    }
    nodeB->prev = node;