title: Javascript breaks getting timezone without DST
body: <p>I'm trying to set a user's timezone offset for PHP, being sent over ajax.  A page has been loaded with session data. If there is no data this gets put into the page:</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
      $(document).ready(function() {
          var visitortime = new Date();
          visitortime.setMonth(1);
          var visitortimezone = visitortime.getTimezoneOffset()*60;
          $.ajax({
              url: "/ajax/timezone/set/"+ visitortimezone,
              success: function(){
                 location.reload();
              }
          });
      });
  &lt;/script&gt;
  </code></pre>
  
  <p>without the <code>visitortime.setMonth(1);</code> it runs fine and returns the right offset. But with it, it returns only 0.</p>
  
  <p>I want to be able to get timezone offset without DST and then run DST check on the PHP side.</p>