YARN-2219. Changed ResourceManager to avoid AMs and NMs getting exceptions after RM recovery but before scheduler learns about apps and app-attempts. Contributed by Jian He.
svn merge --ignore-ancestry -c 1611222 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1611223 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6690. Deduplicate xattr names in memory. (wang)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1611227 13f79535-47bb-0310-9956-ffa450edef68