MAPREDUCE-4637. Handle TaskAttempt diagnostic updates while in the NEW and UNASSIGNED states. (Mayank Bansal via tgraves)

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svn merge -c 1443257 FIXES: MAPREDUCE-4822. Unnecessary conversions in History Events. Contributed by Chu Tong


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1443271 13f79535-47bb-0310-9956-ffa450edef68