[schemaserial] be robust against duplicated CWUniqueTogetherConstrain entities arising from bug in the pre 3.18 era
Closes #4619278.
# -*- coding: utf-8 -*-# copyright %(year)s %(author)s, all rights reserved.# contact %(author-web-site)s -- mailto:%(author-email)s#%(long-license)s"""%(distname)s views/forms/actions/components for web ui"""