message: more descriptive assertion failure for overflow
diff: @@ -80,7 +80,7 @@ where
  }
  let old_revision = self.shared_state.revision.fetch_add(1, Ordering::SeqCst);
  - assert!(old_revision != usize::max_value());
  + assert!(old_revision != usize::max_value(), "revision overflow");
  let result = Revision {
  generation: 1 + old_revision as u64,
  };
  