bug#16920: 24.3; fix eldoc-message to clear own message only

[Stefan Monnier]

> The bug happens when exit minibuffer so we need to clear its state
> thoroughly at exit time. How about something like this:
[...]
> -               (lambda () (setq eldoc-mode-line-string nil))
> +               (lambda () (setq eldoc-mode-line-string nil
> +                           ;; http://debbugs.gnu.org/16920
> +                           eldoc-last-message nil))

Sounds good, thanks,


        Stefan