MAPREDUCE-5974. Allow specifying multiple MapOutputCollectors with fallback. (Todd Lipcon via kasha)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1619496 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6890. Merging change r1619500 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1619501 13f79535-47bb-0310-9956-ffa450edef68