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


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svn merge -c 1577647 FIXES: 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/branches/branch-2@1577648 13f79535-47bb-0310-9956-ffa450edef68
YARN-1717. Enabled periodically discarding old data in LeveldbTimelineStore. Contributed by Billie Rinaldi.
svn merge --ignore-ancestry -c 1577693 ../../trunk/


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svn merge -c 1577692 FIXES: MAPREDUCE-5570. Map task attempt with fetch failure has incorrect attempt finish time. Contributed by Rushabh S Shah


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svn merge -c 1577710 from trunk for HADOOP-10407. Fix the javac warnings in org.apache.hadoop.ipc package.


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