mm-encode: quoted-printable for PDF

[David Kuehling]

The mm-encode functions choose eihter base64 or quoted-printable
encoding for most files based on which encoding is smaller. This does
NOT work with PDF files. For some PDF files quoted-printable is actually
smaller. But when encoding into quoted-printable in Emacs and decoding
on systems (like M$ Win) that use a different end-of-line encoding, all
LF characters of the PDF file are converted to CRLF. After that
procedure the PDF file is really broken!

So I suggest you add

    ("application/pdf" base64)

to `mm-content-transfer-encoding-defaults'. Or (much better and safer)
you make make `mm-encode' use base64 for unknown content:

    (".*" base64))

                                                           David Kühling