make pred customable in auto-save-visited-mode

[纪秀峰 <jixiuf@qq.com>]

When I enable  auto-save-visited-mode and start an ediff merge session 
It always prompt me save "*ediff-merge*” to a file.
 


(define-minor-mode auto-save-visited-mode
  "Toggle automatic saving to file-visiting buffers on or off.
With a prefix argument ARG, enable regular saving of all buffers
visiting a file if ARG is positive, and disable it otherwise.
Unlike `auto-save-mode', this mode will auto-save buffer contents
to the visited files directly and will also run all save-related
hooks.  See Info node `Saving' for details of the save process.

If called from Lisp, enable the mode if ARG is omitted or nil,
and toggle it if ARG is `toggle'."
  :group 'auto-save
  :global t
  (when auto-save--timer (cancel-timer auto-save--timer))
  (setq auto-save--timer
        (when auto-save-visited-mode
          (run-with-idle-timer
           auto-save-visited-interval :repeat
           #'save-some-buffers :no-prompt
           (lambda ()  ;;<————————————how about make this customable
             (not (and buffer-auto-save-file-name
                       auto-save-visited-file-name)))))))