bug#37829: 27.0.50; Overlay behaviour changed without documentation.

[Eli Zaretskii]

> Date: Sun, 20 Oct 2019 16:49:10 +0800
> From: Zhu Zihao <all_but_last@163.com>
> 
> 1. open a empty buffer, type "Lorem ipsum" in it, then goto point-min
> 2. Eval this code
> 
> (let ((ov (make-overlay (point-min) (1+ (point-at-eol)))))
>   (overlay-put ov 'face 'mode-line))
> 
> In current version of Emacs, the mode line overlay will only cover the string
> "Lorem ipsum", but in 26.2, the overlay will cover the hole line(every pixel 
> in
> line).
> 
> It may be a bug because no documentation or NEWS mentioned this change.

Crystal ball says it's because the mode-line face doesn't have the
:extend attribute by default.  If so, this change _is_ in NEWS and in
the ELisp manual.

Thanks.