Add Savepoint support, implement for PostgreSQL only
OPENJPA-2419: Possible fix using Savepoints
OPENJPA-2418: Fix checkstyle to run with maven 3.x.

git-svn-id: https://svn.apache.org/repos/asf/openjpa/branches/2.2.x@1511418 13f79535-47bb-0310-9956-ffa450edef68