libs: add Deref, DerefMut impls for references, fixing a bug in compiler in the process that was blocking this.

Fixes #18621.

src/test/run-pass/deref-mut-on-ref.rs

@@ -0,0 +1,21 @@
+// 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.
+
+// Test that `&mut T` implements `DerefMut<T>`
+
+fn inc<T:DerefMut<int>>(mut t: T) {
+    *t += 1;
+}
+
+fn main() {
+    let mut x: int = 5;
+    inc(&mut x);
+    assert_eq!(x, 6);
+}

src/test/run-pass/deref-on-ref.rs

@@ -0,0 +1,25 @@
+// 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.
+
+// Test that `&T` and `&mut T` implement `Deref<T>`
+
+fn deref<U:Copy,T:Deref<U>>(t: T) -> U {
+    *t
+}
+
+fn main() {
+    let x: int = 3;
+    let y = deref(&x);
+    assert_eq!(y, 3);
+
+    let mut x: int = 4;
+    let y = deref(&mut x);
+    assert_eq!(y, 4);
+}