Update CHANGES.txt to show MR-5688 pulled into 2.4.0


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1577586 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5769. Unregistration to RM should not be called if AM is crashed before registering with RM. Contributed by Rohith


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1577647 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5570. Map task attempt with fetch failure has incorrect attempt finish time. Contributed by Rushabh S Shah


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1577692 13f79535-47bb-0310-9956-ffa450edef68
YARN-1717. Enabled periodically discarding old data in LeveldbTimelineStore. Contributed by Billie Rinaldi.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1577693 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10407. Fix the javac warnings in org.apache.hadoop.ipc package.


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