OAK-527: permissions (wip)

- consistency between isGranted and hasPrivileges as well as getTreePermissions vs. getPrivileges
- change compiled permissions to only take immutable tree (see above)
- prevent access to permission store

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1533341 13f79535-47bb-0310-9956-ffa450edef68