file helper adjusted , upgrade notes added

framework/UPGRADE.md

@@ -47,3 +47,5 @@ Upgrade from Yii 2.0 Beta
 
 * 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`.

framework/helpers/BaseFileHelper.php

@@ -120,16 +120,16 @@ class BaseFileHelper
      */
     public static function getMimeType($file, $magicFile = null, $checkExtension = true)
     {
-        if (function_exists('finfo_open')) {
         $info = finfo_open(FILEINFO_MIME_TYPE, $magicFile);
+
         if ($info) {
             $result = finfo_file($info, $file);
             finfo_close($info);
+
             if ($result !== false) {
                 return $result;
             }
         }
-        }
 
         return $checkExtension ? static::getMimeTypeByExtension($file) : null;
     }