Fixing CHANGES.txt, moving HADOOP-8815 to 2.6.0 release
Fix up CHANGES.txt for HDFS-6134, HADOOP-10150 and related JIRAs following merge to branch-2

Conflicts:
	hadoop-common-project/hadoop-common/CHANGES.txt
	hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
	hadoop-mapreduce-project/CHANGES.txt

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt