Calling a _.debounced function should return the timeout

Currently there is no way to clear a debounced function that has been called. This
is problematic for something like a Backbone view where we need to stop everything
as soon as remove is called. Here is what the changes will let us do:

    class MyApp.MyView extends Backbone.View
        
        initialize: ->
            @doStuffSoon = _(@doStuff).debounce(2000)

        someEvent: ->
            @doStuffTimeout = @doStuffSoon()

        remove: ->
            clearTimeout(@doStuffTimeout)

        doStuff: ->
            # This should never be called after the view has been removed
            alert('stuff!')