+ copy all files and directories in <skeldir> to new user's home
directory, not just if they begin with a '.'
+ use pax to copy files from <skeldir>, as this will allow <skeldir>
to contain directory trees as well as regular files
+ use -h arg to chown(1) in case any symlinks have been created in the
new user's home directory
+ getpwnam(3) does not set errno, so use errx(3) and warnx(3)
+ use nologin(8) in preference to false(1) when deleting users but
preserving information
+ in usage messages, specify [-r lowuid..highuid] rather than a simple
[-r range]
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