rollup merge of #19838: shepmaster/invariant-lifetime-copy

Both ContravariantLifetime and CovariantLifetime are marked as Copy,
so it makes sense for InvariantLifetime to be as well.

src/libcore/kinds.rs

@@ -252,11 +252,9 @@ pub mod marker {
     /// and this pointer is itself stored in an inherently mutable
     /// location (such as a `Cell`).
     #[lang="invariant_lifetime"]
-    #[deriving(Clone, PartialEq, Eq, PartialOrd, Ord)]
+    #[deriving(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
     pub struct InvariantLifetime<'a>;
 
-    impl<'a> Copy for InvariantLifetime<'a> {}
-
     /// A type which is considered "not sendable", meaning that it cannot
     /// be safely sent between tasks, even if it is owned. This is
     /// typically embedded in other types, such as `Gc`, to ensure that