CAY-1794 Duplicate attributes in discriminator columns of PersistentDescriptor

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/branches/STABLE-3.1@1446643 13f79535-47bb-0310-9956-ffa450edef68
CAY-1794 Duplicate attributes in discriminator columns of PersistentDescriptor

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/branches/STABLE-3.1@1446644 13f79535-47bb-0310-9956-ffa450edef68