title: prototype setAttribute() not working with $$() selector
body: <p>I want to change the button onclick function inside a div. The HTML code is as bellow</p>
  
  <pre><code>&lt;div class="buttons-set" id="payment-buttons-container"&gt;
      &lt;button type="button" class="button" onclick="payment.save()" id="payment_button"&gt;&lt;/button&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I am using the following prototype to change the onlick function payment.save() to something else.</p>
  
  <pre><code>if(payment_method=='gate') {
     var e = $$('div#payment-buttons-container button.button');
     e.setAttribute('onclick','return false;'); // not working
  } else {
      var e = $$('div#payment-buttons-container button.button');
      e.setAttribute('onclick','payment.save();'); // not working
  }
  </code></pre>
  
  <p>Which is not working and saying "Uncaught TypeError: Object [object HTMLButtonElement] has no method 'setAttribute'"But when i am using this code by taking the id of the button statically, than its working </p>
  
  <pre><code>if(payment_method=='gate') {
      $('payment_button').setAttribute('onclick','return false;');// Works
  }
  else {
      $('payment_button').setAttribute('onclick','payment.save();');// Works
  }
  </code></pre>
  
  <p>Where "payment_button" is the ID of the button which i taken.</p>