TYPO3 Core

The extension manager should have functions to check if an extension is local, global or system:

public static function isLocalExtension($key) {}
...

Actually the function extPath already does that, so the 3 functions only need to be extracted:

if (@is_dir(PATH_typo3conf . 'ext/' . $key . '/';) {
...

While doing that the @-signs prefixing is_dir should be removed, because i dont see why they are (still?) necessary.