empty XML elements serialized incorrectly

DOMElement.xml serializes empty XML elements incorrectly.

Note: the original env.js (http://github.com/jeresig/env-js... did handle this more correctly:

get outerHTML(){

  var ret = "<" + this.tagName, attr = this.attributes;

  for ( var i in attr )
    ret += " " + i + "='" + attr[i] + "'";

  if ( this.childNodes.length || this.nodeName == "SCRIPT" )
    ret += ">" + this.childNodes.outerHTML + 
      "</" + this.tagName + ">";
  else
    ret += "/>";

  return ret;
},