[DEV-1371] Add USE_TZ setting to settings.py and settings.py.mustache.
[DEV-1371] Amend add_tz_offset filter to use timezone-aware objects.
[DEV-1371] Replace all (uncommented) instances of datetime.datetime.now with timezone.now. Modify imports to accomodate this change.
[DEV-1371] Add timezone-aware migrations module. Replace calls to datetime.datetime.now with calls to timezone.now.
[DEV-1371] Replace specific calls to datetime with calls to timezone.
[DEV-1371] Replace imports of datetime with import of django.utils.timezone in new migrations module.
[DEV-1371_new_migrations] Add tzinfo argument to datetime calls that is set to UTC if 'USE_TZ' is True in settings or None otherwise.
[DEV-1371_new_migrations] Overwrite existing migrations with new timezone-aware migrations.
[DEV-1371_new_migrations] Add missing timezone import.
[DEV-1371] Continue replacing imports and usage of datetime.now with timezone.now.
[DEV-1371] Update django_authopenid migrations to use timezone.now instead of datetime.now.
[DEV-1371] Update group_messaging migrations to use timezone.now instead of datetime.now.
[DEV-1371] Update askbot migrations to make use of south.utils.datetime_utils instead of manually-added tzinfo.
[DEV-1371] Revert to old migrations files.
[DEV-1371] Update migrations to use south.utils.datetime_utils.datetime instead of datetime.datetime.
[DEV-1371] Revert migrations for forked askbot dependencies.
[DEV-1371] Update migrations for deps to use south.utils.datetime_utils.datetime instead of datetime.datetime.
[DEV-1371] Mend add_tz_offset in templatetags to handle aware or naive datetime objects.
[DEV-1371] Add utility function for determining tzinfo according to USE_TZ setting.
[DEV-1371] Use get_tzinfo throughout, where appropriate.