bug#15214: 24.3.50; `Revert This Session's Customization' does not do what it says

[Eli Zaretskii]

> From: Mauro Aranda <maurooaranda@gmail.com>
> Date: Wed, 1 Jan 2020 11:47:45 -0300
> Cc: 15214@debbugs.gnu.org
> 
> > You should instead click "Set to Backup Value".  The Revert button is
> > in general for variables you have saved for future sessions.
> 
> For user options that are of boolean type, that works well.  But for
> other kinds of user options, there is a risk it won't work:
> 
> 1. emacs -Q
> 2. M-x customize-variable dired-kept-versions
> 3. Edit the field to 3 and then Set for current session.
> 4. Now edit it to 4, and then Set for current session.
> 
> Now "Set to Backup Value" won't ever take you back to the state before
> your session's customizations.

"Set to Backup Value" reverts to the previous value, not to the
original one.  So this is working as intended.

> 
> >> The function that runs for that option is custom-variable-reset-saved,
> >> and the doc string of custom-variable-reset-saved says something similar.
> >
> > The doc string is ambiguous, and the code definitely does NOT intend
> > to reset the value, just to remove the recorded setting, so that it
> > won't be saved in the custom file.  That code was installed in
> 
> What part of the doc string do you find ambiguous?

The "reset" part.

> I still think it would be a good addition to the code.  In case you are
> OK with it, I attach a patch with moves the funcall outside of the
> if-else form.

It LGTM, thanks.