fade does include the root element

The FadeMixin does not do anything when `this.getDOMNode()` element has a
fade. This causes a bug at least in the Modal when the `backdrop=false` and `animation=true`. see [here](http://jsfiddle.net/Hhc8z/11/)
and the Modal component is the root, causing it to never fade in.

the PR includes the root element in the list of elements searched, similar to `jQuery.addBack()`. Also added tests (albeit ugly ones)!