title: Laravel 5.2 validation check if value is not equal to a variable
body: <p>In my instance one user is inviting another I would like to check if the user they are inviting is not themselves.</p>
  
  <p>Thus I have two variables <em>incomming email</em> and <em>user->email</em></p>
  
  <pre><code>$this-&gt;validate($request, [
              'email' =&gt; 'required|email',
          ]);
  </code></pre>
  
  <p>How can I add that validation rule to the validation call?</p>