message: tag futures as must use
diff: @@ -70,6 +70,7 @@ impl Client {
  }
  }
  +#[must_use = "futures do nothing unless polled"]
  pub struct Connection(proto::Connection);
  impl Connection {
  @@ -91,6 +92,7 @@ impl Future for Connection {
  }
  }
  +#[must_use = "futures do nothing unless polled"]
  pub struct Handshake(proto::HandshakeFuture);
  impl Future for Handshake {
  @@ -104,6 +106,7 @@ impl Future for Handshake {
  }
  }
  +#[must_use = "futures do nothing unless polled"]
  pub struct Prepare(proto::PrepareFuture);
  impl Future for Prepare {
  