allow the user to install using a Numeric GID or UID.
this brings it in to line with chgrp and chown, ans is required
by some people using FreeBSD in a product.
time of the target if the target file is the same as the source),
-d (debug), and -p (same as -C except for preserving the modification
time of the source if the target doesn't exists or is different from
the source.
Use library err() functions instead of our own and pass them better
exit codes.
Submitted by: wollman (and changed a lot by me)
