UnicodeEncodeError with non-ascii headers

[davidszotten]

Hi.

I'm trying to upgrade to celery 4 which, in particular includes reprs of args and kwargs in headers. however, it seems librabbitmq fails to handle non-ascii headers

>>> import kombu
>>> from kombu import Connection
>>> conn = Connection("librabbitmq://rabbitmq")
>>> channel = conn.channel()
>>> channel.basic_publish('', headers={'key': 'ö'})

UnicodeEncodeError: 'ascii' codec can't encode character '\xf6' in position 0: ordinal not in range(128)

am i doing something wrong? (We rely on this library for the performance compared to the pure python version)

best, and thanks!