MAPREDUCE-5997. native-task: Use DirectBufferPool from Hadoop Common. Contributed by Todd Lipcon.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/MR-2841@1613034 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-6000. native-task: Simplify ByteBufferDataReader/Writer. Contributed by Todd Lipcon.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/MR-2841@1613036 13f79535-47bb-0310-9956-ffa450edef68