Initial (non-functional) code.

- Kill Externalities Error type requirement.

substrate/executor/src/error.rs

@@ -17,7 +17,6 @@
 //! Rust executor possible errors.
 
 use serializer;
-use state_machine;
 
 error_chain! {
 	foreign_links {
@@ -38,9 +37,9 @@ error_chain! {
 		}
 
 		/// Externalities have failed.
-		Externalities(e: Box<state_machine::Error>) {
+		Externalities {
 			description("externalities failure"),
-			display("Externalities error: {}", e),
+			display("Externalities error"),
 		}
 
 		/// Invalid index.