YARN-759. Create Command enum in AllocateResponse (bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1490470 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4862. SafeModeInfo.isManual() returns true when resources are low even if it wasn't entered into manually. Contributed by Ravi Prakash.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1490486 13f79535-47bb-0310-9956-ffa450edef68