bug#57400: 29.0.50; Support sending patches from VC directly

[Eli Zaretskii <eliz@gnu.org>]

> From: Philip Kaludercic <philipk@posteo.net>
> Cc: larsi@gnus.org,  57400@debbugs.gnu.org,  ane@iki.fi
> Date: Tue, 04 Oct 2022 10:40:23 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Can you ask more specific questions?  Are you looking for a generic
> > way of doing what message-goto-body does?  
> 
> Kind of, I would like to have some function that would place the point
> at the beginning of the message body, no matter what MUA is used.  From
> what I see, the implicit assumption always is that a message is composed
> in a single buffer where the headers are written out at the beginning of
> the buffer, then there is some kind of to detect the end of the headers,
> followed by the body.  But what if a MUA wants to use a separate buffer
> for the headers and the body, placing them in two separate windows?
> What if the headers aren't shown at all?  If I want to handle the
> situation generically, it seems like I would have to take all the design
> decisions into consideration.

Do you happen to know about such MUAs?  mail-user-agent currently
supports just 4 MUAs: do any of them work like above?

We could bite the bullet and make this operation a property of
mail-user-agent, like 'composefunc' we already have (see the doc
string of define-mail-user-agent for the full list).  But if
rfc822-goto-eoh can do the job, maybe it's "good enough"?

> >                                            If so, would
> > rfc822-goto-eoh do the job?
> 
> It doesn't seem to do the same, as in message-mode, it jumps to the
> beginning of the "--text follows this line--" line, not to the line
> after it.

Well, moving one line after that, if this is the line you get to with
that function, is easy.  Don't all MUAs have that line?