bug#23785: Emacs 25: "Undo" overdoes things.

[Eli Zaretskii]

> Date: Fri, 17 Jun 2016 15:02:45 +0000
> From: Alan Mackenzie <acm@muc.de>
> 
> Summary: `undo' is broken in Emacs 25.
> 
> In GNU Emacs 25.0.94.2 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.7)
>  of 2016-06-07 built on acm
> Repository revision: 9d5ccebeba0506f7280662630f0ee85a52c8a327
> Configured using:
>  'configure --with-tiff=no --with-gif=no --with-gpm'
> 
> 1. emacs -Q
> 2. C-x C-f decls-6.cc    ; file is attached.
> 3. Move point to BOL 17.
> 4. C-o, and insert the line "Type var = init;".  Call this line 16½.
> 5. M-x revert-buffer.
> 6. Move point to "[" on L16, and use C-M-k to delete "[3 * peq]".
> 7. C-_.  This restores "[3 * peq]" (correctly) but also reinserts line
>    16½ (which is a bug).

Why does this minor issue deserve to declare 'undo' "broken"?  Looks
like an exaggeration to me.