title: Yii - how to override/extend core file
body: <p>I need to override some yii core files - specifically, CGridColumn.php and CController.php.  I need to make sure that these classes are referenced in my application instead of the core files that they override or extend.  How do I do this?  It's got to be pretty simple but I can't seem to find a documented 'correct' way to do it.</p>