HADOOP-10401. ShellBasedUnixGroupsMapping#getGroups does not always return primary group first (ajisakaa via cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1594717 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6326. Merging change r1594743 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1594746 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6287. Add vecsum test of libhdfs read access times (cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1594752 13f79535-47bb-0310-9956-ffa450edef68