HDFS-6731. Merging change r1612715 from trunk

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YARN-2273. NPE in ContinuousScheduling thread when we lose a node. (Wei Yan via kasha)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1612721 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10855. Allow Text to be read with a known Length. Contributed by Todd Lipcon.

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