title: FacesContext.addMessage() does not show message in p:messages
body: <p>i have a managed bean with a method that add a message like this:</p>
  
  <pre><code>@ManagedBean
  @ViewScoped
  public class FileMB implements Serializable{
  
  private static final long serialVersionUID = -2843716026642626725L;
  
  private UploadedFile file;
  private boolean enabled = false;
  
  public UploadedFile getFile() {
      return file;
  }
  
  public void setFile(UploadedFile file) {
      this.file = file;
  }
  
  public void upload() {
  
      FacesMessage message = new FacesMessage("test");
      FacesContext.getCurrentInstance().addMessage(null, message);
  
  }
  </code></pre>
  
  <p>i call this method from xhtml:</p>
  
  <pre><code>&lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;
   &lt;html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:p="http://primefaces.org/ui"&gt;
  &lt;h:head&gt;
      &lt;title&gt;&lt;/title&gt;
  &lt;/h:head&gt;
  &lt;h:body&gt;
  &lt;h:form&gt;
      &lt;p:commandButton value="Show" type="button" actionListener="#{fileMB.upload}" /&gt;
  &lt;/h:form&gt;
   &lt;h:form id="frmMensajes"&gt;
      &lt;p:messages id="mensajes" showDetails="false"/&gt;
  &lt;/h:form&gt;
  &lt;/h:body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>but i cant see the "test" message, i added the managed bean declaration in faces-config too, what could i do?</p>