For now, always signal that a connection should be destroyed rather than retained.  This should clean out every pool at polling time, and permit connections that share the same connection bins to be allocated fairly.  Part of CONNECTORS-872.

git-svn-id: https://svn.apache.org/repos/asf/manifoldcf/trunk@1564151 13f79535-47bb-0310-9956-ffa450edef68