Bug#742668: cups: Fails to install because can't listen to sockets

[Giuseppe Bilotta <giuseppe.bilotta@gmail.com>]

Package: cups
Version: 1.7.2-3
Followup-For: Bug #742668

I've just come across this issue during a dist-upgrade. The situation is the same as
that of the original message: nothing is using port 631 or the cups socket, but:

May 06 14:12:51 labrador systemd[1]: Starting CUPS Printing Service Sockets.
May 06 14:12:51 labrador systemd[1]: cups.socket failed to listen on sockets: Address already in use
May 06 14:12:51 labrador systemd[1]: Failed to listen on CUPS Printing Service Sockets.
May 06 14:12:56 labrador systemd[1]: Closed CUPS Printing Service Sockets.

so cups-daemon, cups and cups-core-drivers fail to complete the upgrade/configure.

-- System Information:
Debian Release: jessie/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.13-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages cups depends on:
ii  cups-client            1.7.2-3
ii  cups-common            1.7.2-3
iu  cups-core-drivers      1.7.2-3
ih  cups-daemon            1.7.2-3
ii  cups-filters           1.0.53-1
ii  cups-ppdc              1.7.2-3
ii  cups-server-common     1.7.2-3
ii  debconf [debconf-2.0]  1.5.53
ii  ghostscript            9.05~dfsg-8.1
ii  libavahi-client3       0.6.31-4
ii  libavahi-common3       0.6.31-4
ii  libc-bin               2.18-5
ii  libc6                  2.18-5
ii  libcups2               1.7.2-3
ii  libcupscgi1            1.7.2-3
ii  libcupsimage2          1.7.2-3
ii  libcupsmime1           1.7.2-3
ii  libcupsppdc1           1.7.2-3
ii  libgcc1                1:4.9.0-2
ii  libstdc++6             4.9.0-2
ii  libusb-1.0-0           2:1.0.18-2
ii  lsb-base               4.1+Debian12
ii  poppler-utils          0.24.5-3
ii  procps                 1:3.3.9-4

Versions of packages cups recommends:
ii  avahi-daemon                     0.6.31-4
ii  colord                           1.0.6-1
ii  cups-filters [ghostscript-cups]  1.0.53-1
ii  printer-driver-gutenprint        5.2.9-2

Versions of packages cups suggests:
ii  cups-bsd               1.7.2-3
ii  cups-pdf               2.6.1-9
ii  foomatic-db            20140325-1
ii  hplip                  3.14.1-1
ii  printer-driver-hpcups  3.14.1-1
ii  smbclient              2:4.1.7+dfsg-2
ii  udev                   204-10

-- debconf information:
* cupsys/backend: lpd, socket, usb, snmp, dnssd
* cupsys/raw-print: true