b2 backend: dies with unicode error

[az]

this is a forward of debian bug #830896, which lives over there: http://bugs.debian.org/830896

the original reporter "created a Backblaze B2 Cloud Storage account and tried to use it with
duplicity. However all duplicity commands using B2 fail for me with the same
error messages:

/usr/lib/python2.7/dist-packages/duplicity/backends/b2backend.py:211: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal
  if bucket_name not in bucket_names:
FatalBackendException: Bucket cannot be created"