title: jQuery.ajax() uses current page URL instead of specified URL
body: <p>If I make this call on a page such as index.php:</p>
  
  <pre><code>jQuery.ajax("keepalive.php");
  </code></pre>
  
  <p>jQuery makes a request for index.php instead of keepalive.php.</p>
  
  <p>This request is only to keep a session going, so I don't care about the result.  According to <a href="http://api.jquery.com/jQuery.ajax/" rel="nofollow">the docs</a>, simply specifying a URL is all that is needed.  Any thoughts on why this doesn't work correctly?</p>