[Nmh-workers] Format function to create wrapped header lines?

[Ken Hornstein]

So, things are plodding along closer to 1.7 release; I think we're getting
close to integrating the XOAUTH2 code on the master branch, so I wanted
to bring up something that I noticed recently.

Our default replcomps generate a References header for threading.  That's
good!  But it turns out that it just appends the message-id to the existing
header without wrapping ... and if you get into a long email thread, that
can exceed the maximum email header limit.  This seems like poor behavior.

It seems we should do something like what formataddr/putaddr does, except
handle an arbitrary set of tokens; I do not believe that we can do it with
the existing mh-format instructions, so some new ones would be required.

Thoughts?

--Ken