Added a test case for #1303

Hi @spicyj

Not sure how I could update my last pull request, so I created a new one. I added a test case for issue #1303 that would fail with "TypeError: Cannot read property 'parentNode' of undefined" if you undo the fix in file src/browser/ui/dom/DOMChildrenOperations.js I noticed a few other tests failing with the same error as well. I tested this with your queue-mc branch and got:

```
>> not ok 405 - core/__tests__/ReactRemoveNodeAndParent-test Removing a node and its parent at the same time Does not try to remove node from parent when parent has already been removed.
# TypeError: 'undefined' is not an object (evaluating 'updatedChildren[j].parentNode') in http://127.0.0.1:9999/test/index.html (line 137)
```