message: Don't send finality signatures we already know of.
diff: @@ -191,6 +191,10 @@ impl<I> LinearChain<I> {
  // TODO: disconnect from the sender.
  break;
  }
  + if block.proofs().contains_key(&fs.public_key) {
  + // Don't send finality signatures we already know of.
  + continue;
  + }
  block.append_proof(fs.public_key, fs.signature);
  let message = Message::FinalitySignature(fs.clone());
  effects.extend(effect_builder.broadcast_message(message).ignore());
  