Test suite fails in chroots

Hi,

DejaGNU's test suite fails when run in a chroot.  We observe this in
NixOS' chroot builds (http://nixos.org/) and similar reports were
already made in the past:

  http://lists.gnu.org/archive/html/bug-dejagnu/2003-06/msg00002.html
  http://thread.gmane.org/gmane.linux.distributions.nixos/1036

The "send: spawn id exp0 not open" appears to stem from the fact that
the file descriptor used by `send_user' is closed at this point.
Any idea how to fix it?

Thanks in advance,
Ludovic.