improving message/rfc822 part handling

[Jameson Graef Rollins <jrollins@finestructure.net>]

So the following patch series is my attempt to improve handling of
message/rfc822 parts.  The first couple of patches fix/overhaul the
multipart test, and the last two improve the message/rfc822 part
output and emacs handling, respectively.

The fix outputs the rfc822 message in a format similar to that of the
outer message, including "headers" and "body" fields.

What this doesn't yet address is the raw output of message/rfc822
parts.  The raw output of message/rfc822 parts /should/ be the full
raw message.  However, I have not yet figured out how to do that yet,
so the multipart test for raw message/rfc822 parts is not yet fixed.

The problem is really gmime's handling of message parts.  There
doesn't seem to be a gmime function that will return the message part
as a GMimeObject.  This means that we can't access all the message
headers, or the messages sub parts as mime objects.  There may be a
way to hack around gmime's limitations, but I haven't figured it out
yet.  If someone else wants to take a crack at it, that would be
great.  In the mean time, I'm opening a bug report with gmime to
request a function to return the rfc822 part as a GMimeObject.

jamie.