message: Checked url matches state before update
  It's possible that 2 links are clicked before either commits. When the second commits then both set state updater functions are called, but only want the second one to run. Don't want to push 2 browser history records.
diff: @@ -29,9 +29,11 @@ class NavigationHandler extends React.Component<{ stateNavigator: StateNavigator
  }
  return null;
  }, () => {
  + if (url === this.state.stateNavigator.stateContext.url) {
  stateNavigator.stateContext = this.state.stateNavigator.stateContext;
  stateNavigator.offNavigate(this.navigateHandler);
  stateNavigator.notify(historyAction);
  + }
  });
  };
  }
  