HDFS-2976. Move attribution to release 2.6.0 section in CHANGES.txt.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1609849 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-8158. Move attribution to release 2.6.0 section in CHANGES.txt.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1609854 13f79535-47bb-0310-9956-ffa450edef68