Upgrade to JSDOM 0.4.1 (which defaults to DOM4 API).

* Updated package.json to JSDOM 0.4.x.

* Fixed code crashes and bugs from the upgrade.
  - node.getAttribute("foo") returns null instead of ''
    if the node does not have 'foo' as the attribute.
  - node.childNodes does not respond to 'slice' anymore.
    Used Util.clone(node.childNodes) instead.

* No change in parser test results.

* Tested roundtrip-test.js, node server, rt-testing
  client and server.  No crashes encountered.

Change-Id: I5703e6454c7c86fcb72a054365f358a426cc8903