title: jQuery .is(':checked') always returns false
body: <p>No mater if the radio button is checked or not, .is(':checked') will return false.  Here is some stuff I was playing with in Chrome's console while I was debugging this:</p>
  
  <pre><code>&gt; $('#blah')
  [&lt;input type=​"radio" id=​"blah" name=​"blah_type" value=​"blah" class=​"styled" checked=​"checked"&gt;​]
  &gt; $('#blah').removeAttr('checked')
  [&lt;input type=​"radio" id=​"blah" name=​"blah_type" value=​"blah" class=​"styled"&gt;​]
  &gt; $('#blah').is(':checked')
  false
  &gt; $('#blah').prop('checked', true)
  [&lt;input type=​"radio" id=​"blah" name=​"blah_type" value=​"blah" class=​"styled"&gt;​]
  &gt; $('#blah').is(':checked')
  false
  &gt; $('#blah').prop('checked')
  true
  &gt; $('#blah').removeProp('checked')
  [&lt;input type=​"radio" id=​"blah" name=​"blah_type" value=​"blah" class=​"styled"&gt;​]
  &gt; $('#blah').attr('checked', true)
  [&lt;input type=​"radio" id=​"blah" name=​"blah_type" value=​"blah" class=​"styled" checked=​"checked"&gt;​]
  &gt; $('#blah').attr('checked')
  "checked"
  &gt; $('#blah').prop('checked')
  undefined
  &gt; $('#blah').is(':checked')
  false
  </code></pre>
  
  <p>What could be going wrong here?  I'm using jQuery 1.6.4. </p>