OAK-1350 : Inconsistent Principal Validation between API and Import behavior

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1560428 13f79535-47bb-0310-9956-ffa450edef68
minor improvement (simplify subclassing)

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1560429 13f79535-47bb-0310-9956-ffa450edef68