OPENJPA-2437: transactional listeners added too late to observe begin event - back ported Mark Struber's changes to 2.2.1.x.

git-svn-id: https://svn.apache.org/repos/asf/openjpa/branches/2.2.1.x@1584153 13f79535-47bb-0310-9956-ffa450edef68