title: header nocache not working as expected
body: <p>The header on my site script includes the following:</p>
  
  <pre><code>header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
  header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
  header("Cache-Control: no-store, no-cache, must-revalidate");
  header("Cache-Control: post-check=0, pre-check=0", false);
  header("Pragma: no-cache");
  </code></pre>
  
  <p>These lines are called prior to any output/whitespace. </p>
  
  <p>This is what is showing in my live header viewer:</p>
  
  <pre><code>POST /includes/whosonline.php HTTP/1.1
  Host: mysite.org
  User-Agent: Linux/Firefox 11
  Accept: text/javascript, text/html, application/xml, text/xml, */*
  Accept-Language: en-us,en;q=0.5
  Accept-Encoding: gzip, deflate
  Connection: keep-alive
  X-Requested-With: XMLHttpRequest
  X-Prototype-Version: 1.6.0.2
  Content-Type: application/x-www-form-urlencoded; charset=UTF-8
  Referer: https://mysite.org?id=123
  Content-Length: 0
  Cookie: [cookie stuff removed]
  Pragma: no-cache
  Cache-Control: no-cache
  </code></pre>
  
  <p>Note that the headers of the script specify that the browser not cache the page.  The Expires date is before the current date.  </p>
  
  <p>Why is this not working?</p>