title: Facebook API - uids and email
body: <p>I am trying to develop a application where </p>
  
  <ol>
  <li>The user 'X' has logged into Facebook</li>
  <li>app has a set of email addresses (possible friends of user 'X')</li>
  <li>app gets the list of friends of user 'X' (uids)</li>
  <li>Want to check if user with email address some@some.com is a valid facebook user by using email address and is user X's friend (basically a uid to email mapping)</li>
  </ol>