Avoid memory leaks during refresh - DO NOT MERGE

This is intended to get some discussion around a solution for memory leaks around elements that are removed during a refresh (http://bugs.jqueryui.com/ticket/10056).

Unfortunately, I don't think there's a general solution we can apply. Every widget that handles a refresh will need to manually track the removed elements and pass them to `._off()`.
I think we'll continue to be limited to just a handful of these uses (likely just this one place for all of UI), so it's probably not worth adding a new method for it. This should be a pretty fast operation as is, especially with how few objects we're working with.