Fixed concurrency problem in HiveHistory.java (contributed originally by @kayousterhout)
Fix bug of boolean equals() method, the reference comparison works incorrectly after deserialization.

Originally contributed by @chenghao-intel
Fix NullPointerException for Constant Null value

Originally contributed by @chenghao-intel
Reduce lock contention in ExprNodeGenericFuncEvaluator and ShimLoader.

Originally contributed by @chenghao-intel.
HIVE-4647 : RetryingHMSHandler logs too many error messages (Navis via Ashutosh Chauhan)

git-svn-id: https://svn.apache.org/repos/asf/hive/trunk@1498149 13f79535-47bb-0310-9956-ffa450edef68