message: reset last_rr_sent on error
  Indicate that setting the RR was a failure and that hitting the API should be retried (in the case where the errcode !== "M_UNRECOGNISED")
diff: @@ -546,6 +546,7 @@ var TimelinePanel = React.createClass({
  });
  }
  // it failed, so allow retries next time the user is active
  + this.last_rr_sent_event_id = undefined;
  this.last_rm_sent_event_id = undefined;
  });
  