[entity] Entity.related(): add a targettypes argument (closes #2957313) This allows to restrict the entity types returned by the method (passed to cw_related_rql). When such an argument is given, no caching happens.

# -*- 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 schema"""