HADOOP-8712. Change default hadoop.security.group.mapping to JniBasedUnixGroupsNetgroupMappingWithFallback. Contributed by Robert Parker.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1433625 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9217. Merging change 1433713 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1433717 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9106. Merge 1433747 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1433752 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4288. NN accepts incremental BR as IBR in safemode. Contributed by Daryn Sharp.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1433756 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-4924. flakey test: org.apache.hadoop.mapred.TestClusterMRNotification.testMR. (rkanter via tucu)

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Merge branch 'branch-2' of github.com:griddynamics/yhadoop-common into branch-2-gd