Convert all keys of the dict 'd' to (ascii-)strings.

    :Raises: UnicodeEncodeError

def clean_dict_keys(d):
    """Convert all keys of the dict 'd' to (ascii-)strings.

    :Raises: UnicodeEncodeError
    """
    new_d = {}
    for (k, v) in d.iteritems():
        new_d[str(k)] = v
    return new_d