HADOOP-9334. Upgrade netty version. Contributed by Nicolas Liochon.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1450463 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4249: optimize counter increments, no need to traverse the tracking structures from top down on every increment
HDFS-4249: defensive check around floating point math to keep percentages in the range [0.0, 1.0]
Merge branch 'trunk' into HDFS-4249