Fix 8bit test

pgp_mime_lib/rfc3156.py

@@ -156,7 +156,7 @@ def encode_base64(msg):
     # now, if content is already encoded as base64 or if it is encoded with
     # some unknown encoding, we just pass.
     if encoding in [None, 'quoted-printable', 'x-uuencode',
-                    'uue', 'x-uue', '7bit']:
+                    'uue', 'x-uue', '7bit', '8bit']:
         orig = msg.get_payload(decode=True)
         encdata = _bencode(orig)
         msg.set_payload(encdata)