* uip/sendsbr.c: with attachformat values of 1 or 2, only

* uip/sendsbr.c: with attachformat values of 1 or 2, only
generate Content-Disposition headers for MIME attachments, not
for the message contents themselves.  Microsoft Outlook Build
10.0.6626, at least, doesn't show the message contents if they
have Content-Disposition.