OAK-709: Consider moving permission evaluation to the node state level

Calculate the readState directly when a SecureNodeState is instantiated
(may need to make it lazy again later, TBD) so we can add the getChildNode()
optimization where we return a fully readable leaf node state directly
without a SecureNodeState wrapper.

Also streamline the property access methods to avoid duplicate
checks when possible.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1465664 13f79535-47bb-0310-9956-ffa450edef68