Derive std::cmp::Reverse as Copy or Clone

If the type parameter is Copy or Clone, then `Reverse` should be too.

src/libcore/cmp.rs

@@ -343,7 +343,7 @@ impl Ordering {
 /// v.sort_by_key(|&num| (num > 3, Reverse(num)));
 /// assert_eq!(v, vec![3, 2, 1, 6, 5, 4]);
 /// ```
-#[derive(PartialEq, Eq, Debug)]
+#[derive(PartialEq, Eq, Debug, Copy, Clone)]
 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
 pub struct Reverse<T>(#[stable(feature = "reverse_cmp_key", since = "1.19.0")] pub T);