#8 Handling bad MIME encodings

[Ken Causey]

For my second patch in 2 days here's one to deal with
the situation in which a message's specified
Content-Transfer-Encoding is not one of the valid choices:

'As stated in the definition of the
Content-Transfer-Encoding field
[RFC 2045], no encoding other than "7bit", "8bit",
or "binary" is
permitted for entities of type "multipart".'

RFC2046 Section 5.1
(ftp://ftp.isi.edu/in-notes/rfc2046.txt)

As is usually the case, Microsoft just can't cooperate
and their .NET system seems to want to send out
messages with parts specifying:

Content-type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7-bit

M$ just can't spell I guess.

Anyway, this patch treats any encodings that
mimetools.decode chokes on as not needing decoding and
just returns that body of the part as is.

[Ken Causey]

Handle mimetools.decode barfing on bad encoding