HDFS-6614. Merging change r1608846 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1608847 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10781. Unportable getgrouplist usage breaks FreeBSD (Dmitry Sivachenko via Colin Patrick McCabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1608871 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6638. Merging change r1608905 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1608911 13f79535-47bb-0310-9956-ffa450edef68
move HADOOP-10781 to 2.6

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1608935 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6627. Merging change r1608940 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1608948 13f79535-47bb-0310-9956-ffa450edef68