[dataimport] Fix use of _create_copyfrom_buffer() (related to #3845572)
This is used indirectly by SQLGenObjectStore when running on a
PostgreSQL database.
Regression introduced by commit 70056633085c.
# -*- coding: utf-8 -*-
# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
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"""%(distname)s entity's classes"""