Toggle saving of minibuffer history (Savehist mode).
With a prefix argument ARG, enable Savehist mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
the mode if ARG is omitted or nil.
When Savehist mode is enabled, minibuffer history is saved
periodically and when exiting Emacs. When Savehist mode is
enabled for the first time in an Emacs session, it loads the
previous minibuffer history from `savehist-file'.
This mode should normally be turned on from your Emacs init file.
Calling it at any other time replaces your current minibuffer
histories, which is probably undesirable. (fn &optional ARG)
Non-nil if Savehist mode is enabled.
See the command `savehist-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `savehist-mode'.