v2 pre-gmime-3.0 cleanup

[David Bremner]

this obsoletes the series at

     id:20170521124821.23924-1-david at tethera.net

Compared to the previous series, it contains a leak fix for
g_mime_stream_stdout_new(), the actual leak fixes promised in the last
patch of the previous series, and modifications to some of the
multipart tests so that headers are no longer expected when printing
multipart bodies; as discussed in

	  id:878tlpyyfi.fsf at tethera.net

and confirmed with gmime upstream, that behaviour can be considered a
bug in gmime-2.6, and goes away in gmime-3.0