Add HDFS-7148 to CHANGES.txt, branch-2 only commit.
HADOOP-11140. hadoop-aws only need test-scoped dependency on hadoop-common's tests jar. Contributed by Juan Yu.
MAPREDUCE-5831. Make MR client ignore unknown counters received from AM. Contributed by Junping Du.
CHANGES.txt: move HDFS-6584 and its subtasks to Release 2.6.0.
HDFS-6956. Allow dynamically changing the tracing level in Hadoop servers (cmccabe)
YARN-2577. Clarify ACL delimiter and how to configure ACL groups only (Mikos Christine via aw)
Merge branch 'trunk' into HDFS-6581