Limit the number of transactions in pending set (#8777)

* Unordered iterator.

* Use unordered and limited set if full not required.

* Split timeout work into smaller timers.

* Avoid collecting all pending transactions when mining

* Remove println.

* Use priority ordering in eth-filter.

* Fix ethcore-miner tests and tx propagation.

* Review grumbles addressed.

* Add test for unordered not populating the cache.

* Fix ethcore tests.

* Fix light tests.

* Fix ethcore-sync tests.

* Fix RPC tests.

ethcore/light/src/net/tests/mod.rs

@@ -173,8 +173,8 @@ impl Provider for TestProvider {
 		})
 	}
 
-	fn ready_transactions(&self) -> Vec<PendingTransaction> {
-		self.0.client.ready_transactions()
+	fn ready_transactions(&self, max_len: usize) -> Vec<PendingTransaction> {
+		self.0.client.ready_transactions(max_len)
 	}
 }