OPENJPA-2459.  Revert back to Java 6 in preparation for an interim release before embarking on JPA 2.1 and Java 7 and the rest of Java EE 7...

git-svn-id: https://svn.apache.org/repos/asf/openjpa/trunk@1599775 13f79535-47bb-0310-9956-ffa450edef68