Fix --preserve-root

[Arcterus]

I'm fairly certain that if the --preserve-root in chgrp was wrong, it is wrong in other utilities as well.

[wimh]

chgrp will still follow a bind mount to root and continue:

mkdir /root/root
mount -o bind / /root/root
chgrp --preserve-root -R root /root -v

The same applies to a symbolic link (with -H).

ln -s / /root/root
./target/debug/deps/chgrp --preserve-root -R root /root -v -H

Though it will detect a file system loop if a symbolic link is pointing to a parent directory other than the root directory (ln -s /tmp /tmp/tmp).

[Arcterus]

I'm pretty sure the problem right now is because we are only checking if it's a bind mount to root or a symbolic link to root in traverse(), which is only called once. The WalkDir in dive_into() doesn't check for either of these cases, so it just keeps going unless you specifically give a bind mount to root or a symbolic link on the command-line.

[stale]

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