Generics fixes

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/dbcp/trunk@1537613 13f79535-47bb-0310-9956-ffa450edef68
TODO - privatise mutable fields as far as possible

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/dbcp/trunk@1537615 13f79535-47bb-0310-9956-ffa450edef68