Merge -c 1527848 from trunk to branch-2 to fix MAPREDUCE-5551. Fix compat with hadoop-1 in SequenceFileAsBinaryOutputFormat.WritableValueBytes by re-introducing missing constructors. Contributed by Zhijie Shen.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1527850 13f79535-47bb-0310-9956-ffa450edef68