bug#20930: 25.0.50; Package archive priorities not honored for upgrades

[Greg Lucas]

The new package archive priorities to not appear to be honored when I
check for available upgrades.

Steps to reproduce:

1. Start emacs -Q

2. configure-group package

 -  Add melpa and melpa-stable to package-archives:

    (("gnu" . "http://elpa.gnu.org/packages/";)
     ("melpa-stable" . "http://stable.melpa.org/packages/";)
     ("melpa" . "http://melpa.org/packages/";))

 -  Set priorities with melpa-stable highest:

    (("melpa-stable" . 20))

3. list-packages and install something from melpa-stable for which there
is a newer version on melpa. In my test: ace-jump-mode v2.0.

  ace-jump-mode      2.0           installed

4. Check for upgrades; get prompted to upgrade to melpa version:

I ace-jump-mode      20140616.115  available  melpa
D ace-jump-mode      2.0           installed

Since melpa has priority 0 and melpa-stable has priority 20, I would
expect this upgrade not to be included. In my current setup I have a
dozen or so packages from the gnu and melpa-stable archives and am
prompted to update all of them. 




In GNU Emacs 25.0.50.1 (x86_64-w64-mingw32)
 of 2015-06-19 on KAEL
Repository revision: f95211e9a40b1c7d1beff0e15aa67450f80bd8bb
Windowing system distributor `Microsoft Corp.', version 6.3.9600
Configured using:
 `configure --prefix=/z/emacs --host=x86_64-w64-mingw32
 --target=x86_64-w64-mingw32 --build=x86_64-w64-mingw32 --with-wide-int
 --with-jpeg --with-xpm --with-png --with-tiff --with-rsvg --with-xml2
 --with-gnutls --with-sound=yes --with-file-notification=yes
 --without-dbus --without-imagemagick 'CFLAGS=-O3 -fomit-frame-pointer
 -g0 -pipe' 'LDFLAGS=-static-libgcc -static-libstdc++ -static -s
 -Wl,-s''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1252

Major mode: Package Menu

Minor modes in effect:
  tooltip-mode: t
  global-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
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Type C-x 1 to delete the help window.
Quit
Importing package-keyring.gpg...done
Package refresh done
12 packages can be upgraded; type `U' to mark them for upgrading.
M-o C-x 1 is undefined
Quit [2 times]
12 packages marked for upgrading.
Making completion list...
Quit

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mailabbrev gmm-utils mailheader
sendmail pp help-mode package-x misearch multi-isearch mail-utils
network-stream nsm starttls url-http tls mail-parse rfc2231 rfc2047
rfc2045 ietf-drums url-gw url-cache url-auth url url-proxy url-privacy
url-expand url-methods url-history url-cookie url-domsuf url-util
url-parse auth-source cl-macs cl-seq eieio byte-opt gv bytecomp
byte-compile cl-extra seq cconv eieio-core gnus-util mm-util mail-prsvr
password-cache url-vars mailcap epg finder-inf package epg-config
help-fns cus-edit easymenu cus-start cus-load wid-edit cl-loaddefs pcase
cl-lib time-date mule-util tooltip eldoc electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel dos-w32 ls-lisp disp-table w32-win
w32-vars term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment elisp-mode lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core 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 charscript case-table epa-hook jka-cmpr-hook help
simple abbrev 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
w32notify w32 multi-tty make-network-process emacs)

Memory information:
((conses 16 751841 24023)
 (symbols 56 25662 0)
 (miscs 48 722 215)
 (strings 32 68718 9681)
 (string-bytes 1 1511638)
 (vectors 16 23760)
 (vector-slots 8 536819 5652)
 (floats 8 204 257)
 (intervals 56 89643 864)
 (buffers 976 17))