HADOOP-10489. UserGroupInformation#getTokens and UserGroupInformation#addToken can lead to ConcurrentModificationException. Contributed by Robert Kanter.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1596027 13f79535-47bb-0310-9956-ffa450edef68
Reverting HADOOP-10485 from branch-2.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1596041 13f79535-47bb-0310-9956-ffa450edef68