YARN-2755. NM fails to clean up usercache_DEL_<timestamp> dirs after YARN-661. Contributed by Siqi Li
(cherry picked from commit 73e626ad91cd5c06a005068d8432fd16e06fe6a0)
HDFS-7165. Separate block metrics for files with replication count 1. Contributed by Zhe Zhang.
HADOOP-11250. fix endmacro of set_find_shared_library_without_version in CMakeLists (Yi Liu via Colin P. McCabe)
(cherry picked from commit e488f0d93bf22d25aaaac7a6a88fc300f9aa6d5a)
HDFS-7230. Add rolling downgrade documentation. Contributed by Tsz Wo Nicholas Sze.

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
HADOOP-11221. IdentityHashStore assumes System.identityHashCode() is non-negative. Contributed by Jinghui Wang
HDFS-3342. SocketTimeoutException in BlockSender.sendChunks could have a better error message. Contributed by Yongjun Zhang.

(cherry picked from commit 16c0f04c50822a39610e34e0715d3d4a44be5a5f)
update CHANGES.txt to move HADOOP-11247 to 2.6
YARN-2677 registry punycoding of usernames doesn't fix all usernames to be  DNS-valid (stevel)
HDFS-7035. Make adding a new data directory to the DataNode an atomic operation and improve error handling (Lei Xu via Colin P. McCabe)
(cherry picked from commit a9331fe9b071fdcdae0c6c747d7b6b306142e671)
HDFS-6385. Show when block deletion will start after NameNode startup in WebUI. Contributed by Chris Nauroth.

(cherry picked from commit c637d6d9d5cb36b8cd5180787c5d25b68f2aa370)
HDFS-7313. Support optional configuration of AES cipher suite on DataTransferProtocol. Contributed by Chris Nauroth.

(cherry picked from commit 5573b3476a5a6fce0ac99c654a9a9ec90f744a20)
YARN-2698. Moved some node label APIs to be correctly placed in client protocol. Contributed by Wangda Tan.

(cherry picked from commit e0233c16ebd06bb3aabeb523cd17259008e243ef)
YARN-2779. Fixed ResourceManager to not require delegation tokens for communicating with Timeline Service. Contributed by Zhijie Shen.

(cherry picked from commit d1828d94435eca21761b0ba8458f9de2f125d012)
Merge remote-tracking branch 'remotes/origin/branch-2' into branch-2