OAK-593: Segment-based MK

Keep the RecordId available for SegmentNodeStates and SegmentStreams so we can avoid storing duplicate copies of records that already exist.
Also fix MapEntry comparison code.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1444612 13f79535-47bb-0310-9956-ffa450edef68