'Load messages previously saved to S3.'

def load_from_s3(self, bucket, prefix=None):

    n = 0
    if prefix:
        prefix = ('%s/' % prefix)
    else:
        prefix = ('%s/' % self.id[1:])
    rs = bucket.list(prefix=prefix)
    for key in rs:
        n += 1
        m = self.new_message(key.get_contents_as_string())
        self.write(m)
    return n
