Bug#807671: 20copyfiles doesn't cope well with absolute symlinks in destination path

[Florian Schlichting <fsfs@debian.org>]

this is now https://gitlab.com/codelibre/schroot/merge_requests/20 and
was merged to master two years ago.

However, this still doesn't fix the issue I face when entering a schroot
of main system, with

    /etc/resolv.conf -> /run/NetworkManager/resolv.conf

$ schroot -c thinkpad -u root
E: 20copyfiles: realpath: /run/schroot/mount/thinkpad-7b8f67af-f952-4f84-be1d-07ef66e9249a/run/NetworkManager/resolv.conf: No such file or directory
E: 20copyfiles: cp: cannot create regular file '': No such file or directory
E: thinkpad-7b8f67af-f952-4f84-be1d-07ef66e9249a: Chroot setup failed: stage=setup-start

BTW without that patch, it looks like this:

$ schroot -c thinkpad -u root
E: 20copyfiles: cp: '/etc/resolv.conf' and '/var/run/schroot/mount/thinkpad-fe82a8ce-cf15-4cbb-928c-dfabea3eebbd/etc/resolv.conf' are the same file
E: thinkpad-fe82a8ce-cf15-4cbb-928c-dfabea3eebbd: Chroot setup failed: stage=setup-start