Sync reorg up to history size (#3874)

* Allow sync reorg up to pruning history size

* Peer difficulty tracking

* Abort downloading block if received with NewBlock

* Set pruning history to 1200

* Renamed history size field

ethcore/src/client/test_client.rs

@@ -92,6 +92,8 @@ pub struct TestBlockChainClient {
 	pub first_block: RwLock<Option<(H256, u64)>>,
 	/// Traces to return
 	pub traces: RwLock<Option<Vec<LocalizedTrace>>>,
+	/// Pruning history size to report.
+	pub history: RwLock<Option<u64>>,
 }
 
 /// Used for generating test client blocks.
@@ -154,6 +156,7 @@ impl TestBlockChainClient {
 			ancient_block: RwLock::new(None),
 			first_block: RwLock::new(None),
 			traces: RwLock::new(None),
+			history: RwLock::new(None),
 		};
 		client.add_blocks(1, EachBlockWith::Nothing); // add genesis block
 		client.genesis_hash = client.last_hash.read().clone();
@@ -314,6 +317,11 @@ impl TestBlockChainClient {
 		let res = res.into_iter().next().unwrap().expect("Successful import");
 		assert_eq!(res, TransactionImportResult::Current);
 	}
+
+	/// Set reported history size.
+	pub fn set_history(&self, h: Option<u64>) {
+		*self.history.write() = h;
+	}
 }
 
 pub fn get_temp_state_db() -> GuardedTempResult<StateDB> {
@@ -704,6 +712,7 @@ impl BlockChainClient for TestBlockChainClient {
 		PruningInfo {
 			earliest_chain: 1,
 			earliest_state: 1,
+			state_history_size: *self.history.read(),
 		}
 	}