HBASE-12337 Import tool fails with NullPointerException if clusterIds is not initialized
HBASE-12449 Use the max timestamp of current or old cell's timestamp in HRegion.append()
HBASE-12411 Optionally enable p-reads and private readers for compactions.
HBASE-12517 Ensure HConstants members are final.

Signed-off-by: stack <stack@apache.org>

Conflicts:
	hbase-common/src/main/java/org/apache/hadoop/hbase/HConstants.java

Conflicts:
	hbase-common/src/main/java/org/apache/hadoop/hbase/HConstants.java
HBASE-12513 Graceful stop script does not restore the balancer state

Signed-off-by: stack <stack@apache.org>
HBASE-12496 A blockedRequestsCount metric (Yi Deng)