OAK-535: MergeCommand reads complete tree into memory
- special case trivial merges when there were no commits to trunk in the meantime

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1433336 13f79535-47bb-0310-9956-ffa450edef68
Fixed oak-mongomk-perf in light of the recent API change in oak-mongomk

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1433340 13f79535-47bb-0310-9956-ffa450edef68