title: Call to undefined function yii\helpers\mb_strlen() even though mbstring is enabled
body: <p>I have enabled mbstring in my php.ini.It even shows in phpinfo().But still I am getting this error in yii2.</p>
  
  <pre><code>PHP Fatal Error 'yii\base\ErrorException' with message 'Call to undefined function yii\helpers\mb_strlen()
  </code></pre>