The current behaviour of "notmuch show --part=1 --raw" is somewhat
peculiar. This is supposed to be the message body, but if the message is
multipart, it also includes the headers. This seems to be a direct
translation of an implimentation of quirk of gmime. In gmime 3.0 this
quirk goes away, and the behaviour of notmuch consequently changes,
unless we do something about it. I actually think the new behaviour
makes more sense (you only get the headers with part=0). There seem to
be several options

1) Bug-for-Bug-compatibility: Add special case code for gmime-3.0 to
   output headers.

2) Allow-varying-output: Consider the previous behaviour a bug, fixed by
   using gmime-3.0.  This makes it hard for people to rely on, although
   how one relies on it currently since it varies by message is a
   mystery.

3) Fix the alleged bug: special case the output of the body with
   gmime-2.6 to avoid outputting headers.

d