This only happens if USE_TZ = False and pytz is installed (perhaps not
the most logical combination, but who am I to jugde?)
Refs #23714 which essentially fixed the same problem when USE_TZ = True.
Thanks Florian and Carl for insisting until I wrote a complete patch.
Modified django.utils.dateformat module, moving __init__() method and
timezone-related format methods from DateFormat class to TimeFormat
base class. Modified timezone-related format methods to return an
empty string when timezone is inappropriate for input value.