#1435 Proxy the view's el on the behavior in addition to $el

To address @jmeas's [concerns](https://github.com/marionettejs/backbone.marionette/issues/1435#issuecomment-45174398), Backbone.View  only creates a new `el` if one isn't provided at construction (`_ensureElement`). 
Maybe a test where the behavior adds an attribute or triggers an event on either the $el and el the el, and both the behavior and the view see the attribute or hear the event. This is more of an integration test than what you have, but with behaviors, I've found that that's helpful because the delegation can act in unexpected ways.