Make supertrait references work in object types too.

src/test/run-pass/associated-type-doubleendediterator-object.rs

@@ -0,0 +1,27 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn pairwise_sub(mut t: Box<DoubleEndedIterator<Item=int>>) -> int {
+    let mut result = 0;
+    loop {
+        let front = t.next();
+        let back = t.next_back();
+        match (front, back) {
+            (Some(f), Some(b)) => { result += b - f; }
+            _ => { return result; }
+        }
+    }
+}
+
+fn main() {
+    let v = vec!(1, 2, 3, 4, 5, 6);
+    let r = pairwise_sub(box v.into_iter());
+    assert_eq!(r, 9);
+}