OAK-1392: SegmentBlob.equals() optimization

Reuse previous property records if the value(s) have not changed.
This optimizes the case where a binary value is rewritten without changes.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1567586 13f79535-47bb-0310-9956-ffa450edef68