OAK-708: SecureNodeState#getChildNodeCount and #getPropertyCount: don't respect read permissions

Streamline SecureNodeState.getPropertyCount() to use the minimum amount of work when possible.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1465644 13f79535-47bb-0310-9956-ffa450edef68