OPENJPA-2373: MapsId in a Child entity to a Parent entity using auto-assigned identity fails with duplicte INSERT SQL - back ported to 2.1.x Pinaki Poddar's trunk changes.

git-svn-id: https://svn.apache.org/repos/asf/openjpa/branches/2.1.x@1484300 13f79535-47bb-0310-9956-ffa450edef68