OAK-2039 SegmentNodeStore might not create a checkpoint
 - merged rev 1619815



git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1619819 13f79535-47bb-0310-9956-ffa450edef68
OAK-2040 Tar compaction: log a warning if there is more than one checkpoint
 - merged rev 1619823, 1619824



git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/branches/1.0@1619826 13f79535-47bb-0310-9956-ffa450edef68