EIP-168, 169: Dust protection (#4757)

* Dust protection

* Track touched accounts in the substate

* Minor alterations

ethcore/src/error.rs

@@ -165,6 +165,8 @@ pub enum BlockError {
 	InvalidNumber(Mismatch<BlockNumber>),
 	/// Block number isn't sensible.
 	RidiculousNumber(OutOfBounds<BlockNumber>),
+	/// Too many transactions from a particular address.
+	TooManyTransactions(Address),
 	/// Parent given is unknown.
 	UnknownParent(H256),
 	/// Uncle parent given is unknown.
@@ -205,6 +207,7 @@ impl fmt::Display for BlockError {
 			UnknownParent(ref hash) => format!("Unknown parent: {}", hash),
 			UnknownUncleParent(ref hash) => format!("Unknown uncle parent: {}", hash),
 			UnknownEpochTransition(ref num) => format!("Unknown transition to epoch number: {}", num),
+			TooManyTransactions(ref address) => format!("Too many transactions from: {}", address),
 		};
 
 		f.write_fmt(format_args!("Block error ({})", msg))