Inconsistent states when there are two events in one cycle

When two events happen "at the same time" (on one event loop), then a state cannot be updated consistently. That can happen with `onClick` on both a parent and a child (event bubbling), as in this example where the final state is not 2, but 1, although both events fire and both messages are handled:

```
(deftest bubbling-events-test
(let [c1 (reacl/class "c1" this state [& more]
render (apply dom/div
{:onclick (fn [ev]
(reacl/send-message! this :foo))}
more)

handle-message
(fn [msg]
(reacl/return :app-state (inc state))))

c2 (reacl/class "c2" this state []
render (c1 (reacl/bind this :x)
(c1 (reacl/bind this :x))))

host (js/document.createElement "div")
cc (reacl/render-component host c2 {:x 0})]

(let [inner-div (.-firstChild (.-firstChild host))]
(react-tu/Simulate.click inner-div (js/Event. "click" #js {:bubbles true :cancelable true})))

(is (= 2 (:x (test-util/extract-app-state cc))))))
```