RFC: dropping privs in chroot --user

[Pádraig Brady]

Both setuidgid and runuser behave as I would expect
and drop the supplemental groups of the root user:

  # runuser padraig -c "id -G"
  500 10 489 491

  # ~padraig/git/coreutils/src/setuidgid padraig id -G
  500 10 489 491

However chroot does not:

  # chroot --user=padraig: / id -G
  500 0 1 2 3 4 6 10

  # chroot --user=padraig / id -G
  0 500 1 2 3 4 6 10

That's at least unexpected and could
be considered a bug I think.
If I'm missing nothing I'll send a patch soon.

thanks,
Pádraig.