Skip . and .. when generating trees.

Fixes #2012

lib/Cake/Utility/Folder.php

@@ -413,6 +413,9 @@ class Folder {
 			if ($skipHidden && $name[0] === '.' || isset($exceptions[$name])) {
 				continue;
 			}
+			if ($name === '.' || $name === '..') {
+				continue;
+			}
 			if ($item->isFile()) {
 				$files[] = $item->getPathName();
 			} else if ($item->isDir()) {