Refine the code according to Jon's comments.
Merge branch 'hbase-11339-core' of https://github.com/JingchengDu/hbase into hbase-11339-core
Merge branch 'hbase-11339-core' into hbase-11339-core-compaction
Merge branch 'hbase-11339-core-compaction' of https://github.com/JingchengDu/hbase into hbase-11339-core-compaction