Fix a contention reported by SUM4JVM

git-svn-id: http://svn.apache.org/repos/asf/commons/proper/dbcp@1568668 13f79535-47bb-0310-9956-ffa450edef68
Fix problem identified while performance testing validation queries.

git-svn-id: http://svn.apache.org/repos/asf/commons/proper/dbcp@1568674 13f79535-47bb-0310-9956-ffa450edef68