HBASE-7929 Reapply hbase-7507 "Make memstore flush be able to retry after exception" to 0.94 branch.

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1451087 13f79535-47bb-0310-9956-ffa450edef68
HBASE-7944 Replication leaks file reader resource & not reset currentNbOperations (Jeffrey Zhong)



git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1451100 13f79535-47bb-0310-9956-ffa450edef68