Allow "None" for conf.TIME_ZONE to avoid calling tzset()

[philz42]

Django defaults (I believe) to Chicago time. It often makes sense to set the time zone explicitly, but, in many applications, the system timezone (typically handled by /etc/localtime magic) is just fine. I'd like to propose that

        if hasattr(time, 'tzset'):
            # Move the time zone info into os.environ. See ticket #2315 for why
            # we don't do this unconditionally (breaks Windows).
            os.environ['TZ'] = self.TIME_ZONE
            time.tzset()

be changed to start

if self.TIME_ZONE is not None and hasattr(time, 'tzset'):
...

That way, if you explicitly set TIME_ZONE to None (this could be the default or not; doesn't matter to me), the system default will get used.

Thoughts?

[Ramiro Morales]

Possibly a duplicate of #1480.

[philz42]

Closing as duplicate of #1480.