title: codeigniter 3 namespacing issue
body: <p>I am working on codeigniter 3. I use composer psr-4 autoload. I enable composer config as 
  <code>$config['composer_autoload'] = FCPATH."vendor/autoload.php";</code> </p>
  
  <p>and my composer.json autoload as</p>
  
  <pre><code>"autoload":{
    "psr-4":{
        "App\\":"application"
          },
    "classmap":["system"]
    }
  }
  </code></pre>
  
  <p>I have an abstract controller as <code>Controller.php</code> as</p>
  
  <pre><code>&lt;?php namespace App\controllers;
  use CI_Controller;
  abstract class Controller extends CI_Controller{}
  </code></pre>
  
  <p>which works fine.
  But The main issue is when I write as controller as</p>
  
  <pre><code>&lt;?php namespace App\controllers;
  use App\controllers\Controller;
  use App\models\User;
  class Welcome extends Controller {
      public function index()
      {
          $this-&gt;load-&gt;view('welcome_message');
      }
  }
  </code></pre>
  
  <p>does not work. If I remove <code>namespace App\Controllers;</code> Everything goes fine.
  Where is the main problem? Thank you.</p>