title: changing email resource.pending_reconfirmation? no longer works with rails 4
body: <p>After upgrading to rails 4, 
  I have problem with </p>
  
  <pre><code>resource.pending_reconfirmation?
  </code></pre>
  
  <p>In registrations#edit view i have:</p>
  
  <pre><code>  - if devise_mapping.confirmable? &amp;&amp; resource.pending_reconfirmation?
      %div
        Currently waiting confirmation for: #{resource.unconfirmed_email}.
        %br
        Please click the link in the email to confirm
    .ruler
  </code></pre>
  
  <p>it seems devise_mapping.confirmable? == true but right after an email change resource.pending_reconfirmation? keeps false.</p>
  
  <p>Why is this happening and how to resolve?</p>