title: [DataTables ][columnFilter] thead:after doesn't work
body: <p>i try to use columFilter with sPlaceHolder: "thead:after"</p>
  
  <p>i use :
  jquery 1.8.1
  datatables 1.9.3
  columnFilter 1.5.0</p>
  
  <p>my table is :</p>
  
  <pre><code>&lt;table align="center" border="1" id="tatable"&gt;
              &lt;thead&gt;
              &lt;tr&gt;
                  &lt;th scope="col"&gt;Numero de la prise&lt;/th&gt;
                  &lt;th scope="col"&gt;Description&lt;/th&gt;
                  &lt;th scope="col"&gt;Piece&lt;/th&gt;
                  &lt;th scope="col"&gt;Action&lt;/th&gt;
              &lt;/tr&gt;
              &lt;tr&gt;
                      &lt;th&gt;&lt;/th&gt;
                      &lt;th&gt;&lt;/th&gt;
                      &lt;th&gt;&lt;/th&gt;
                      &lt;th&gt;&lt;/th&gt;
                  &lt;/tr&gt;
              &lt;/thead&gt;
              &lt;tfoot&gt;
                  &lt;tr&gt;
                      &lt;th&gt;&lt;/th&gt;
                      &lt;th&gt;&lt;/th&gt;
                      &lt;th&gt;&lt;/th&gt;
                      &lt;th&gt;&lt;/th&gt;
                  &lt;/tr&gt;
              &lt;/tfoot&gt;
              &lt;tbody&gt;
  // a lot of data
  &lt;/tbody&gt;
  &lt;/table&gt;
  </code></pre>
  
  <p>my jquery code for initialisation is : </p>
  
  <pre><code>$(document).ready(function(){
  $('#tatable').dataTable({
              "bLengthChange": false,
              "iDisplayLength":50    
  }).columnFilter({
      sPlaceHolder: "thead:after",
      aoColumns :[
          {type: "text"},
          {type: "text"},
          {type: "text"},
          {type: "text"}
      ]
      }
  );
  });
  </code></pre>
  
  <p>this code display 2 row on header and inputs is on bottom of the table ... WHY ??? </p>
  
  <p>(link of jquery plugins )
  <a href="http://www.datatables.net" rel="nofollow">http://www.datatables.net</a> and 
  <a href="http://jquery-datatables-column-filter.googlecode.com/svn/trunk/index.html" rel="nofollow">http://jquery-datatables-column-filter.googlecode.com/svn/trunk/index.html</a></p>