MAPREDUCE-5157. Bring back old sampler related code so that we can support binary compatibility with hadoop-1 sorter example. Contributed by Zhijie Shen.
svn merge --ignore-ancestry -c 1480474 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1480476 13f79535-47bb-0310-9956-ffa450edef68