OAK-2311: Released checkpoint can still be retrieved

- Fix for DocumentNodeStore
- Removed MONGO_MK fixture because the MicroKernel does not have methods for checkpoint release and info. 

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1642816 13f79535-47bb-0310-9956-ffa450edef68
OAK-1907: Better cost estimates for traversal, property, and ordered indexes
Update test expectations so events from oak:index are ignored

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1642825 13f79535-47bb-0310-9956-ffa450edef68
OAK-2291: Associate user defined values with checkpoint

Implementation for DocumentNodeStore

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1642837 13f79535-47bb-0310-9956-ffa450edef68
OAK-2291: Associate user defined values with checkpoint

Fix issue in oak-mongo.js

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1642838 13f79535-47bb-0310-9956-ffa450edef68