Add entry to branch's CHANGES.txt for previous commit

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/MR-2841@1613827 13f79535-47bb-0310-9956-ffa450edef68

hadoop-mapreduce-project/CHANGES.MAPREDUCE-2841.txt

@@ -6,3 +6,4 @@ MAPREDUCE-5994. Simplify ByteUtils and fix failing test. (todd)
 MAPREDUCE-5996. native-task: Rename system tests into standard directory layout (todd)
 MAPREDUCE-5997. native-task: Use DirectBufferPool from Hadoop Common (todd)
 MAPREDUCE-6000. native-task: Simplify ByteBufferDataReader/Writer (todd)
+MAPREDUCE-5991. native-task should not run unit tests if native profile is not enabled. (Binglin Chang)