MAPREDUCE-5166. Fix ConcurrentModificationException due to insufficient synchronization on updates to task Counters. Contributed by Sandy Ryza.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1471635 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9458. Fix RPC.getProxy to ensure it uses retries for getProtocolVersion too. Contributed by Tsz Wo Sze.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1471644 13f79535-47bb-0310-9956-ffa450edef68