pytz.timezone doesn't accept unicode timezone

[Frank Ploss]

When giving a unicode timezone to pytz.timezone(), it throws an exception.

>>> pytz.timezone(u'US/Central')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.6/dist-packages/pytz-2011b-py2.6.egg/pytz/__init__.py", line 154, in timezone
    _tzinfo_cache[zone] = build_tzinfo(zone, open_resource(zone))
  File "/usr/local/lib/python2.6/dist-packages/pytz-2011b-py2.6.egg/pytz/tzfile.py", line 121, in build_tzinfo
    _transition_info=transition_info))
TypeError: type() argument 1 must be string, not unicode

It certainly is easy to circumvent this, but it is annoying having to remember this special constraint as I am using unicode strings throughout the whole program.

[Stuart Bishop (stub)]

This is a regression. Line 146 of pytz/__init__.py used to convert the timezone to ASCII, but this was changed to just confirm the timezone contained just ASCII characters. This was done because the older construct resulted in a bytestring under Python 3.x.