Ability to add custom config for tests

To customize paths to YII and config file for tests now we can create 
tests/config/env.php 
````
<?
return array(
	'config' => dirname(__FILE__) . '/local.php',   // this file will be used as config in tests
	'yiit' => '/home/pahanini/Projects/yii/framework/yiit.php' // this path will be used for yii
);
````