HBASE-7437 Improve CompactSelection (Hiroshi Ikeda)

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1470754 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8384 heap size computation for HStore is fishy

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1470777 13f79535-47bb-0310-9956-ffa450edef68