Add empty account existence test from beta. (#2769)

* add bloom filter existence test from beta

* fix U256 instantiation for master

ethcore/src/state/mod.rs

@@ -1671,6 +1671,21 @@ fn remove() {
 	assert_eq!(state.nonce(&a), U256::from(0u64));
 }
 
+#[test]
+fn empty_account_exists() {
+	let a = Address::zero();
+	let path = RandomTempPath::new();
+	let db = get_temp_state_db_in(path.as_path());
+	let (root, db) = {
+		let mut state = State::new(db, U256::from(0), Default::default());
+		state.add_balance(&a, &U256::default()); // create an empty account
+		state.commit().unwrap();
+		state.drop()
+	};
+	let state = State::from_existing(db, root, U256::from(0u8), Default::default()).unwrap();
+	assert!(state.exists(&a));
+}
+
 #[test]
 fn remove_from_database() {
 	let a = Address::zero();