fix gpg_get_key_addresses

fix gpg_get_key_addresses

Do not use codecs.decode(s, "unicode_escape"). It has two issues:
 * When being passed a bytes literal, the returned value becomes a str
   and the decoding operation is locale specific on Python3.
 * When passing a unicode literal, it implicitly encodes to
   sys.getdefaultencoding() (locale specific) on Python2.
Thus "unicode_escape" is a bad choice in all cases.

For Python2 string_escape works with str, but it hinders a potential
Python3 port of dak. Use it now, because Python3 is totally broken.