HDFS-4804. WARN when users set the block balanced preference percent below 0.5 or above 1.0. Contributed by Stephen Chu.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1480098 13f79535-47bb-0310-9956-ffa450edef68
Move the CHANGES.txt entry for HDFS-4804 from BUG to IMPROVEMENT.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1480101 13f79535-47bb-0310-9956-ffa450edef68