Better Windows detection

build/controllers/AppController.php

@@ -29,7 +29,7 @@ class AppController extends Controller
      */
     protected function unlink($file)
     {
-        if (is_dir($file) && strncasecmp(PHP_OS, 'WIN', 3) === 0) {
+        if (is_dir($file) && DIRECTORY_SEPARATOR === '\\') {
             rmdir($file);
         } else {
             unlink($file);

framework/mutex/FileMutex.php

@@ -70,7 +70,7 @@ class FileMutex extends Mutex
      */
     public function init()
     {
-        if (stripos(php_uname('s'), 'win') === 0) {
+        if (DIRECTORY_SEPARATOR === '\\') {
             throw new InvalidConfigException('FileMutex does not have MS Windows operating system support.');
         }
         $this->mutexPath = Yii::getAlias($this->mutexPath);