Indexes created from datetimes that are tz aware but tz=None (pytz.FixedOffset()) lose tz awareness

[hauptmech]

The index created from datetimes with a FixedOffset tz get converted to the correct UTC time but lose their timezone awareness so that further operations with tz aware datetimes fail.

pytz.FixedOffset() timezones have tzname() return None

[changhiskhan]

changed in tslib.pyx:

function _get_zone will return tz if tz.zone is None (previously just returned tz.zone)