OAK-527: permissions (wip)

- proper handling of OAK_CHILD_ORDER property to only check permissions if a user-supplied reorder occured.
- omit permission check for all items inside a hidden tree otherwise

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1466403 13f79535-47bb-0310-9956-ffa450edef68