javadoc

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1541454 13f79535-47bb-0310-9956-ffa450edef68
OAK-685 Enforce referential integrity for referenceable nodes
 - moved constants into a dedicated class so that the names are available to the outside (like the id manager)

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1541455 13f79535-47bb-0310-9956-ffa450edef68