OAK-144 Implement observation
- Use event filter from the time of the call to onEvent instead of from the time the events are iterated
- Move EventGeneratingValidator to stand alone class and rename to EventGenerator

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1536757 13f79535-47bb-0310-9956-ffa450edef68
OAK-1080: MongoMK: improved concurrency

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1536758 13f79535-47bb-0310-9956-ffa450edef68