function bodyContains($obj) {
	var id = $obj.attr('id'),
		el = id ? env.window.document.getElementById(id) : null;
	// must also check that the element with the id is the one we want
	return el ? el === $obj[0] : $.contains(env.window.document.body, $obj[0]);
}
A fast function to check if an element is still in the DOM. It
tries to use an id as ids are indexed by the browser, or falls
back to jQuery's `contains` method. May fail if two elements
have the same id, but so be it

@param {object} $obj A jQuery-wrapped HTML element
@return {boolean}