setup-translators breaks schroot chroot removal

[Gabriele Giacone <1o5g4r8o@gmail.com>]

Hello,

02schroot.diff [0] patch to get schroot work do bind-mount /dev,
/servers, /proc and additional pathnames, which get umounted when
session terminates. Problem is about /proc and running
setup-translators (e.g. upgrading hurd). It re-sets up bindmounted
/proc:

Start a chroot session.
       -     4     2   ?  0:02.65 /hurd/proc
    root    20     5   -  0:00.18 /hurd/procfs -c
    root  1660     1   -  0:00.01 /hurd/firmlink /proc

Run setup-translator -K.
Then on session end, bindmount correctly gets umounted but a new
procfs makes chroot removal fail:

       -     4     2   ?  0:02.75 /hurd/proc
    root    20     5   -  0:00.22 /hurd/procfs -c
    root  2453     5   -  0:00.00 /hurd/procfs -c

 E: 05file: rm: cannot remove
'/var/lib/schroot/unpack/gg0-file00/proc': Device or resource busy

How to fix it? on setup-translators or on schroot side?

[0] https://lists.debian.org/debian-hurd/2014/09/msg00011.html

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G..e