HBASE-10722 [0.94] HRegion.computeHDFSBlocksDistribution does not account for links and reference files.

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HBASE-10738 AssignmentManager should shut down executors on stop

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1577407 13f79535-47bb-0310-9956-ffa450edef68
HBASE-10642 Add M/R over snapshots to 0.94

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