title: Send devise confirmation email to new email instead of old email
body: <p>By default devise sends confirmation email to <strong>old</strong> email if an email is changed.
  In my case where a user is allowed to create an account via Twitter login, his initial email is blank since Twitter API does not give user's email. Later if user wants to <strong>update</strong> his email id, i want to send him confirmation email on <strong>new</strong> email id since his old email id is blank.</p>
  
  <p>How can I achieve this in devise with confirmation email going to <strong>new</strong> email. I know its a security hole to send confirmation email to new email, but for now we can live with this issue .</p>