Work around bug in "Microsoft Outlook IMO, Build 9.0.2416

Work around bug in "Microsoft Outlook IMO, Build 9.0.2416
(9.0.2910.0)" -- it sends documents of type application/octet-stream
with embedded hard line breaks, which is illegal according to RFC
2045, page 20:

	Since the canonical representation of media types other than
	text do not generally include the representation of line
	breaks as CRLF sequences, no hard line breaks (i.e. line
	breaks that are intended to be meaningful and to be displayed
	to the user) can occur in the quoted-printable encoding of
	such types.