bug fix: allow symlinks when coping existing files to chroot

symptom:

when etc/debootstrap/etc/... were symlinks:

 /bin/chroot-script: line 52: /etc/apt/sources.list: Too many levels of symbolic links

justification, quoting from mlist:

"please add '--dereference' whenever 'cp' files from host into chroot
system. I want to symlink them into /etc/debootstrap/etc/ instead of copying
them over."