Fields must render values in the current time zone.
This commit only contains tests because this ticket was just a symptom of
a regression from #18777 that was fixed separately.
This commit deprecates django.utils.tzinfo in favor of the more recent
django.utils.timezone which was introduced when Django gained support
for time zones.
This also updates all dependent functionality, including modelform_factory
and modelformset_factory, and the generic views `ModelFormMixin`,
`CreateView` and `UpdateView` which gain a new `fields` attribute.
Claude Paroz
Aymeric Augustin
Roberto Aguilar
Luke Plant
Florian Apolloner