HDFS-4462. 2NN will fail to checkpoint after an HDFS upgrade from a pre-federation version of HDFS. Contributed by Aaron T. Myers.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1442378 13f79535-47bb-0310-9956-ffa450edef68
svn merge -c 1442386 from trunk for HADOOP-9252. In StringUtils, humanReadableInt(..) has a race condition and the synchronization of limitDecimalTo2(double) can be avoided.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1442387 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'branch-2' of github.com:griddynamics/yhadoop-common into branch-2-gd