var myrules = {

  'a.link-external' : function(element){
    element.onclick = function() {      
      var linkto = this.href;
      this.href = "javascript:void(0);";
      window.open(linkto,'links');
    }
  },
  
  'a.link-thumbnail-external' : function(element){
    element.onclick = function() {
      var linkto = this.href;
      this.href = "javascript:void(0);";
      window.open(linkto,'links');
    }
  }
  
};
  
Behaviour.register(myrules);