alloc: Fix the fmt::Pointer impl for Box

Author: richo

src/liballoc/boxed.rs

@@ -278,7 +278,10 @@ impl<T: fmt::Debug + ?Sized> fmt::Debug for Box<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> fmt::Pointer for Box<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        fmt::Pointer::fmt(&*self, f)
+        // It's not possible to extract the inner Uniq directly from the Box,
+        // instead we cast it to a *const which aliases the Unique
+        let ptr: *const T = &**self;
+        fmt::Pointer::fmt(&ptr, f)
     }
 }