extract the right parent directory from the path

add parent directory to the file cache if it does not exist yet.

lib/filecache.php

@@ -79,7 +79,7 @@ class OC_FileCache{
 
 		// add parent directory to the file cache if it does not exist yet.
 		if ($parent == -1 && $fullpath != $root) {
-			$parentDir = substr(dirname($path), 0, strrpos(dirname($path), DIRECTORY_SEPARATOR));
+			$parentDir = dirname($path);
 			self::scanFile($parentDir);
 			$parent = self::getParentId($fullpath);
 		}