[dom] Pull Request: Fix another NodeIterator removing step

Joris-van-der-Wel has just submitted a new pull request for 
https://github.com/whatwg/dom:

== Fix another NodeIterator removing step ==
This change makes it more consistent with the other rules. Also,
it is what the w3c test suite expects and how the browsers behave.

Here's a quick snippit to test:
```javascript
document.body.innerHTML = "<p>Efghijkl</p><p>Mnopqrst</p>";
var it = document.createNodeIterator(document);
while (it.nextNode());

var removed = document.body.children[1];
removed.parentNode.removeChild(removed);

console.info(it.referenceNode === 
document.body.children[0].lastChild);
console.info(it.pointerBeforeReferenceNode === false);
```

See https://github.com/whatwg/dom/pull/27