Button icon span

Working branch right now up for functional review for button re-write demo at http://view.jqueryui.com/button-icon-span/demos/button/

Spec: http://wiki.jqueryui.com/w/page/71756381/Button
These two lines could be chained, since both start with `this.element`.

Also I'm wondering about that `blur()` call. I guess a disabled element can't be focused, so it won't do anything. Though should we make sure that the element is actually focussed before trying to blur it? Should be easy enough using `document.activeElement`.