Implement EIP-1052 (EXTCODEHASH) and fix several issues in state account cache (#9234)

* Implement EIP-1052 and fix several issues related to account cache

* Fix jsontests

* Merge two matches together

* Avoid making unnecessary Arc<Vec>

* Address grumbles

ethcore/src/client/client.rs

@@ -1339,7 +1339,7 @@ impl BlockInfo for Client {
 	}
 
 	fn code_hash(&self, address: &Address, id: BlockId) -> Option<H256> {
-		self.state_at(id).and_then(|s| s.code_hash(address).ok())
+		self.state_at(id).and_then(|s| s.code_hash(address).unwrap_or(None))
 	}
 }