HDFS-4256 Backport concatenation of files into a single file to branch-1 (sanjay Radia)


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1432185 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-4933. MR1 final merge asks for length of file it just wrote before flushing it. Contributed by Sandy Ryza


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1432243 13f79535-47bb-0310-9956-ffa450edef68