OPENJPA-2505: Properly init MetaDataRepository when obtaining a reference in EntityManagerFactory.getMetaModel.  Back-ported to 2.2.x Rick Curtis' trunk changes.

git-svn-id: https://svn.apache.org/repos/asf/openjpa/branches/2.2.x@1627059 13f79535-47bb-0310-9956-ffa450edef68