bug#33490: 27.0.50; auto-save-visited-mode clears the echo area every time the save interval is hit

[Terje Larsen <terje.larsen@klarna.com>]

M-x auto-save-visited-mode
M-: (message "%s" "hello")

... Wait 5 seconds ...

Now the message buffer gets cleared and you lose the message. This is
causing usability issues when using eldoc/reading some output message as
it continously gets cleared.

I would expect the `auto-save-visited' feature to not change the behaviour
of the Echo Area. If you compare this to the `auto-save-mode' which
outputs a message indicating a save, but restores the Echo Area after.

I have tracked down this to the `save-some-buffers' function or more
specifically the `map-y-or-n-p' function that it calls. In this function
there is a call to message like `(message "")`.


In GNU Emacs 27.0.50 (build 2, x86_64-apple-darwin18.0.0, NS appkit-1671.00 Version 10.14 (Build 18A391))
of 2018-11-07 built on C02V91MHHV2Q.local
Repository revision: 811d9291fcfb12d87bad277d4e8b25152129d73d
Windowing system distributor 'Apple', version 10.3.1671
System Description:  Mac OS X 10.14.1

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Auto-Save-Visited mode enabled
You can run the command ‘auto-save-visited-mode’ with M-x au-v RET
Auto-Save-Visited mode enabled
hello
"hello"
Making completion list... [2 times]

Configured using:
'configure --disable-dependency-tracking --disable-silent-rules
--enable-locallisppath=/usr/local/share/emacs/site-lisp
--infodir=/usr/local/Cellar/emacs/HEAD-811d929_1/share/info/emacs
--prefix=/usr/local/Cellar/emacs/HEAD-811d929_1 --with-gnutls
--without-x --with-xml2 --without-dbus --with-imagemagick --with-rsvg
--with-ns --disable-ns-self-contained'

Configured features:
RSVG IMAGEMAGICK GLIB NOTIFY KQUEUE ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS NS THREADS LCMS2 GMP

Important settings:
  value of $LC_ALL: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t
  auto-save-visited-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
easymenu mml-sec password-cache epa derived epg epg-config gnus-util
rmail rmail-loaddefs time-date mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs cl-lib sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils cus-start
cus-load elec-pair tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/ns-win ns-win ucs-normalize mule-util
term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads kqueue cocoa ns lcms2 multi-tty make-network-process
emacs)

Memory information:
((conses 16 211301 10028)
(symbols 48 20869 1)
(strings 32 30416 1948)
(string-bytes 1 793438)
(vectors 16 35289)
(vector-slots 8 725548 23404)
(floats 8 47 72)
(intervals 56 245 0)
(buffers 992 12))