A utility function to create the 2-tuple (md5hexdigest, base64md5)
        from just having a precalculated md5_hexdigest.

def get_md5_from_hexdigest(self, md5_hexdigest):
        """
        A utility function to create the 2-tuple (md5hexdigest, base64md5)
        from just having a precalculated md5_hexdigest.
        """
        import binascii
        digest = binascii.unhexlify(md5_hexdigest)
        base64md5 = base64.encodestring(digest)
        if base64md5[-1] == '\n':
            base64md5 = base64md5[0:-1]
        return (md5_hexdigest, base64md5)