bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Eli Zaretskii]

> From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
> Date: Mon, 8 Jan 2018 12:43:38 +0000
> 
> Does that mean this patch can't be merged until we've figured a way out by 
> changing `define-minor-mode` to
> introduce a new `buffer-minor-modes` buffer local variable?

We need to figure out some way for desktop.el to record
dired-hide-details-mode, either automatically or given user
customizations.

It's possible that looking at minor-mode-list (not minor-mode-alist!)
is such a way.