Merge remote-tracking branch 'parity/master' into bft

ethcore/src/error.rs

@@ -168,6 +168,8 @@ pub enum BlockError {
 	UnknownParent(H256),
 	/// Uncle parent given is unknown.
 	UnknownUncleParent(H256),
+	/// The same author issued different votes at the same step.
+	DoubleVote(H160),
 }
 
 impl fmt::Display for BlockError {
@@ -201,6 +203,7 @@ impl fmt::Display for BlockError {
 			RidiculousNumber(ref oob) => format!("Implausible block number. {}", oob),
 			UnknownParent(ref hash) => format!("Unknown parent: {}", hash),
 			UnknownUncleParent(ref hash) => format!("Unknown uncle parent: {}", hash),
+			DoubleVote(ref address) => format!("Author {} issued too many blocks.", address),
 		};
 
 		f.write_fmt(format_args!("Block error ({})", msg))