bug#27230: eldoc doc

[Charles A. Roelli]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Fri, 15 Sep 2017 01:03:35 +0300
> 
> > Right.  But why should we break its calling convention without good
> > reason, when we can see that now that other packages have been using
> > it?
> 
> Now they know they should fix it, though.

Unfortunately it means there are probably other users of the function,
and if we don't document the change, the function should stay as is.
Attached is a patch that brings back the old behavior, without the
convoluted buggy logic for setting eldoc-last-message.  What do you
think?

And from an earlier message:

> Aside from breaking the "obviously wrong" callers like explained above, 
> the code had a subtle bug where calling it with no format arguments, and 
> then with some arguments, wouldn't update the message area.

Should be fixed with this patch.

0001-Keep-old-calling-convention-of-eldoc-message.patch
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