* The database table of the `yii\log\DbTarget` now needs a `prefix` column to store context information.
You can add it with `ALTER TABLE log ADD COLUMN prefix TEXT AFTER log_time;`.
* Extension `Fileinfo` added to requirement checker. This extension is [builtin](http://www.php.net/manual/en/fileinfo.installation.php) in php above `5.3`.
* The `fileinfo` PHP extension is now required by Yii. If you use `yii\helpers\FileHelper::getMimeType()`, make sure
you have enabled this extension. This extension is [builtin](http://www.php.net/manual/en/fileinfo.installation.php) in php above `5.3`.
