title: laravel 4.1 unique validation on update fails
body: <p>Laravel 4.1. I want to update a city, check the rules and it fails on unique check.</p>
  
  <p>Rules:</p>
  
  <pre><code>public static $rules = [
      'name' =&gt; 'required|alpha_dash|unique:cities',
      'slug' =&gt; 'alpha_dash|unique:cities',
      'seo_title' =&gt; 'required|max:60|unique:cities',
      'seo_description' =&gt; 'required|max:160|unique:cities',
      'rank' =&gt; 'integer',
      'visible' =&gt; 'integer'
  ];
  </code></pre>
  
  <p>I know, I can smth like:</p>
  
  <pre><code>'name' =&gt; 'required|alpha_dash|unique:cities, name, ##',
  </code></pre>
  
  <p>where ## - id, but I cant dynamically set id to updated one.</p>
  
  <pre><code>'name' =&gt; "required|alpha_dash|unique:cities, name, $id", // doesnt work
  'name' =&gt; "required|alpha_dash|unique:cities, name, $this-&gt;id", // doesnt work
  </code></pre>
  
  <p>Is there any way to do it normally ?</p>