fix bad-caching of datetime with tz info at sql generation time There is a special handling for datetime with tzinfo, where value was stored in the query cache. The implementation of merge_args was simply overwriting parameters of the query with those in the query cache, expecting no collision. To fix this: * handle replacement of tzinfo in merge_args, not at sql generation time * add an assertion to ensure we've actually no collision Closes #6978316

# -*- 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 specific hooks and operations"""