HBASE-9129 Scanner prefetching leaks scanners.

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1511110 13f79535-47bb-0310-9956-ffa450edef68
HBASE-9129 Scanner prefetching leaks scanners. -- MISSED DELETE

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1511116 13f79535-47bb-0310-9956-ffa450edef68