title: p:column header facet is not shown when rendered attribute is used on p:column
body: <p>I have a <code>&lt;p:dataTable&gt;</code>. I would like to render a <code>&lt;p:column&gt;</code> conditionally as follows:</p>
  
  <pre><code>&lt;p:dataTable value="#{abcList}" var="abc"&gt;
    &lt;p:column rendered="#{headerShow}"&gt;
      &lt;f:facet name="header"&gt;
        &lt;h:outputText value="header" /&gt;
      &lt;/f:facet&gt;
      &lt;h:outputText value="#{abc.hijk}" /&gt;
    &lt;/p:column&gt;
  &lt;/p:dataTable&gt;
  </code></pre>
  
  <p>When <code>#{headerShow}</code> is <code>false</code>, then the column is hidden.
  When <code>#{headerShow}</code> is <code>true</code>, then the column is shown, but without header.
  When I hardcode <code>rendered="true"</code>, then the column is shown with header.</p>
  
  <p>How is this caused and how can I solve it?</p>