pub fn push_back(&mut self, t: T) {
// Create the new node, and make it a raw pointer.
let new = Box::new( Node { data: t, next: ptr::null_mut(), prev: self.last } );
let new = box_into_raw(new);
pub fn push_back(&mut self, t: T) {
// Create the new node, and make it a raw pointer.
let new = Box::new( Node { data: t, next: ptr::null_mut(), prev: self.last } );
let new = box_into_raw(new);