Allow many attestation instances to live at once in network (#46)

* multiple consensus sessions in network

* tests compile, add a test for RecentSessionKeys

* track recently received session keys from validators

* add a test for desired key-sending behavior

polkadot/network/src/router.rs

@@ -36,7 +36,8 @@ use std::collections::{HashMap, HashSet};
 use std::io;
 use std::sync::Arc;
 
-use super::{NetworkService, Knowledge};
+use consensus::Knowledge;
+use super::NetworkService;
 
 fn attestation_topic(parent_hash: Hash) -> Hash {
 	let mut v = parent_hash.as_ref().to_vec();
@@ -242,6 +243,13 @@ impl<P: ProvideRuntimeApi + Send> TableRouter for Router<P>
 	}
 }
 
+impl<P> Drop for Router<P> {
+	fn drop(&mut self) {
+		let parent_hash = &self.parent_hash;
+		self.network.with_spec(|spec, _| spec.remove_consensus(parent_hash));
+	}
+}
+
 /// Receiver for block data.
 pub struct BlockDataReceiver {
 	inner: ::futures::sync::oneshot::Receiver<BlockData>,