bug#39960: 28.0.50; Incompatible change to sql-add-product in Emacs 27

[Philipp]

In Emacs 26, sql-add-product has the signature

(sql-add-product PRODUCT DISPLAY &rest PLIST)

However, in the Emacs 27 pretest the signature is now

(sql-add-product PRODUCT DISPLAY &optional PLIST)

Note the change from &rest to &optional.  This is a breaking change that
breaks all users of sql-add-product.  I've found quite a few uses of the
old signature in the wild,
e.g. 
https://github.com/kat-co/sql-prestodb/blob/f4a74d88dcb166445bb41efb865147c0faf1de3a/src/sql-presto.el#L59
or
https://github.com/r0man/vertica-el/blob/3c9647b425c5c13c30bf0cba483646af18196588/vertica.el#L68
or
https://github.com/jterk/sql-impala/blob/466e7c0c789ec3e5e8a276c8f6754f91bb584c3e/sql-impala.el#L71.
This change was introduced in commit
c124d5323c05a4010db9b2d330575d029936ade1.  I don't think we should
introduce such a breaking change to a widely-used public function; at
the very least, Emacs 27 should accept both signatures.


In GNU Emacs 28.0.50 (build 39, x86_64-apple-darwin19.3.0, NS appkit-1894.30 
Version 10.15.3 (Build 19D76))
 of 2020-02-29
Repository revision: 3d2c82ac96a7f37e60b2b85a5c9c1d792084ab54
Repository branch: master
Windowing system distributor 'Apple', version 10.3.1894
System Description:  Mac OS X 10.15.3

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --with-modules --without-xml2 --without-pop --with-mailutils
 --enable-gcc-warnings=warn-only --enable-checking=all
 --enable-check-lisp-object-type 'CFLAGS=-ggdb3 -O0''

Configured features:
NOTIFY KQUEUE ACL GNUTLS ZLIB TOOLKIT_SCROLL_BARS NS MODULES THREADS
JSON PDUMPER LCMS2 GMP

Important settings:
  value of $LANG: de_DE.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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec epa epg epg-config gnus-util
rmail rmail-loaddefs text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils phst skeleton
derived edmacro kmacro pcase ffap thingatpt url-parse auth-source cl-seq
eieio eieio-core cl-macs eieio-loaddefs password-cache json map url-vars
subr-x rx gnutls puny seq byte-opt gv bytecomp byte-compile cconv dbus
xml cl-loaddefs cl-lib 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 tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer 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 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 60470 5746)
 (symbols 48 8045 0)
 (strings 32 20761 1931)
 (string-bytes 1 688813)
 (vectors 16 12996)
 (vector-slots 8 167493 10214)
 (floats 8 27 19)
 (intervals 56 196 0)
 (buffers 1000 11))