Bug#888184: tasksel: freezes if there is a conffile prompt

[Benjamin Moody <benjamin.moody@gmail.com>]

Package: tasksel
Version: 3.39
Severity: normal

Dear Maintainer,

It seems that when installing packages using tasksel, if dpkg needs to
ask the user what to do about a configuration file, the tasksel
process freezes with no explanation.

Example:

  debootstrap stretch /var/chroot/stretch-test http://deb.debian.org/debian/
  chroot /var/chroot/stretch-test
    touch /etc/magic
    tasksel install standard

    => gets to the point of "Configuring libmagic1 (amd64)", and freezes.

Furthermore, tasksel can't be interrupted at that point by ^C, ^Z, or ^\.
It doesn't seem to respond to any terminal input at all.