Use jQuery.contains to check if view.el is in DOM

Instead of [Node.contains](https://developer.mozilla.org/en-US/docs/Web/API/Node.contains). In particular, fixes compatibility with Firefox < 9.
Just a note that Backbone only requires Backbone.$ to be used for dom lookup.  For people using jquery-less Backbone, this won't work. https://github.com/jashkenas/backbone/wiki/Using-Backbone-without-jQuery