title: IceFaces - commandButton doesn't return attatchment
body: <p>CommandButton doesn't return attachment (txt file) from action. I have no errors. Just nothing happend. </p>
  
  <p><strong>Java code:</strong></p>
  
  <pre><code> FacesContext facesContext = FacesContext.getCurrentInstance();
   HttpServletResponse response = (HttpServletResponse)facesContext.getExternalContext().getResponse();
   response.setContentType("application/txt");
   response.setHeader("Content-Disposition","attachment;filename=file.txt");
   IOUtils.copy(new StringReader("TEST"), response.getOutputStream());
   facesContext.responseComplete();
   facesContext.renderResponse();
  </code></pre>
  
  <p><strong>iceFaces - jspx</strong></p>
  
  <pre><code>            &lt;ice:commandButton 
                  id="downloadBtn" 
                  action="#{contentsBean.downloadAsZip}" 
                  value="txt" partialSubmit="true" immediate = "true" &gt;       
              &lt;/ice:commandButton&gt;
  </code></pre>
  
  <p>I try to use commandButton, because i can't use ice:outputResource.</p>