Avoid memory leaks during refresh - DO NOT MERGE

[scottgonzalez]

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().

[scottgonzalez]

This actually shouldn't be too hard to manage, since we're already tracking the elements in each widget. We can either have a conditional like this or initialize all the properties to empty jQuery objects to avoid calling .not() on undefined. We'll just need to go through every widget and make sure we're doing this.

[tjvantoll]

This approach seems sane to me. At the very least I can't think of a better way of avoiding the problem.

If we apply this approach to all widgets, I worry that this could regress fairly easily though. Is there any way we could test this? Something like verifying that references have been removed from bindings, focusable, and hoverable?

[scottgonzalez]

I discussed testing and regressing with @tjvantoll in IRC and we agreed that the chances for regression are fairly low and the tests would need to test private properties from the base widget, so we won't be adding tests for this.

I'm going to close this and put together a new PR with proper commits now that we've agreed on the approach.