MAPREDUCE-5014. Extend Distcp to accept a custom CopyListing. Contributed by Srikanth Sundarrajan

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1459690 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd