title: Yii import or include
body: <p>I encountered a problem about importing php files.</p>
  
  <p>Why this works:</p>
  
  <pre><code>include( Yii::getPathOfAlias( 'ext.payu.payU').'.php' );
  </code></pre>
  
  <p>but that don't:</p>
  
  <pre><code>Yii::import( 'ext.payu.payU');
  </code></pre>
  
  <p>?</p>
  
  <p>file payU.php:</p>
  
  <pre><code>include_once( dirname(__FILE__) . "/sdk/openpayu.php"); //this is a valid path
  class payU{ }
  </code></pre>