OAK-1553: More sophisticated conflict resolution when concurrently adding nodes
Updated contract for addExistingNode conflict

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1580588 13f79535-47bb-0310-9956-ffa450edef68
OAK-1574: AbstractRebaseDiff: Implement refined conflict resolution for addExistingNode conflicts
Implementation of new contract specified in OAK-1553

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1580589 13f79535-47bb-0310-9956-ffa450edef68