Wired character-set decoding into From and Subject

- Removed extra message object from ReadBody() return type
 - We now use enmime's GetHeader() when building the GOB, this will get
   us alternate character set decoding for the From and Subject headers.
 - Added a swaks test with a utf-8 subject line

smtpd/datastore.go

@@ -26,7 +26,7 @@ type Message interface {
 	Subject() string
 	RawReader() (reader io.ReadCloser, err error)
 	ReadHeader() (msg *mail.Message, err error)
-	ReadBody() (msg *mail.Message, body *enmime.MIMEBody, err error)
+	ReadBody() (body *enmime.MIMEBody, err error)
 	ReadRaw() (raw *string, err error)
 	Append(data []byte) error
 	Close() error