OAK-619 Lock-free MongoMK implementation
- MongoDocumentStore.findAndUpdate() must not perform an upsert, otherwise it may happen that a unique key constraint is violated.


git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1475711 13f79535-47bb-0310-9956-ffa450edef68