Jumptable cache (#2427)

* Jumptable cache

* Updated registrar address

ethcore/src/verification/queue/kind.rs

@@ -164,6 +164,7 @@ pub mod headers {
 	}
 
 	/// A mode for verifying headers.
+	#[allow(dead_code)]
 	pub struct Headers;
 
 	impl Kind for Headers {
@@ -179,4 +180,4 @@ pub mod headers {
 			engine.verify_block_unordered(&unverified, None).map(|_| unverified)
 		}
 	}
-}
+}