bug#63627: Improve plstore.el and fix various issues of it

[Eli Zaretskii]

> Date: Thu, 14 Sep 2023 23:24:54 +0200
> Cc: 63627@debbugs.gnu.org
> From: Jens Schmidt <jschmidt4gnu@vodafonemail.de>
> 
> After some consideration actually only one Emacs 29 bug requires fixing.
> Namely that the sequence:
> 
>     (setq plstore (plstore-open plstore-test-file))
>     (plstore-save plstore)
>     (plstore-close plstore)
> 
> silently drops any encrypted data in PLSTORE.  Verified in my local
> master with the new ERT tests, and also verified that the attached patch
> fixes the issue.
> 
> Please consider for committing on emacs-29.

Thanks, but did you mean to say this should not be subsequently merged
to master?  If so, you should tell that in the commit log message.