HADOOP-8415. Add getDouble() and setDouble() in org.apache.hadoop.conf.Configuration (Jan van der Lugt via harsh)
Previous commit merges HADOOP-8415 into branch-2.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1461722 13f79535-47bb-0310-9956-ffa450edef68