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

* Dust protection

* Track touched accounts in the substate

* Minor alterations

ethcore/src/snapshot/tests/proof_of_authority.rs

@@ -124,7 +124,7 @@ fn make_chain(accounts: Arc<AccountProvider>, blocks_beyond: usize, transitions:
 		};
 
 		// execution callback for native contract: push transaction to be sealed.
-		let nonce = RefCell::new(client.engine().account_start_nonce());
+		let nonce = RefCell::new(client.engine().account_start_nonce(0));
 		let exec = |addr, data| {
 			let mut nonce = nonce.borrow_mut();
 			let transaction = Transaction {