Fix several RPCs (#1926)

* Fix up pending receipts details.

* Add support for additional params and registry over RPC.

* Fix tests.

* Add test, additional fix.

Fixes #1932.

* Fix up tests.

* Fix test.

* Fix test.

ethcore/src/engines/mod.rs

@@ -44,6 +44,9 @@ pub trait Engine : Sync + Send {
 	/// Additional engine-specific information for the user/developer concerning `header`.
 	fn extra_info(&self, _header: &Header) -> HashMap<String, String> { HashMap::new() }
 
+	/// Additional information.
+	fn additional_params(&self) -> HashMap<String, String> { HashMap::new() } 
+
 	/// Get the general parameters of the chain.
 	fn params(&self) -> &CommonParams;