message: Use saturating_duration_since for next_delay
  This won't change anything, but it is smaller.
diff: @@ -944,13 +944,9 @@ impl Connection {
  let earliest = delays.into_iter().min().unwrap();
  // TODO(agrover, mt) - need to analyze and fix #47
  // rather than just clamping to zero here.
  - qdebug!(
  - [self],
  - "delay duration {:?}",
  - max(now, earliest).duration_since(now)
  - );
  debug_assert!(earliest > now);
  - let delay = max(now, earliest).duration_since(now);
  + let delay = earliest.saturating_duration_since(now);
  + qdebug!([self], "delay duration {:?}", delay);
  self.hrtime.update(delay / 4);
  delay
  }
  