Switch sample path for black/whitelist files from /var/mail (which is meant to

Switch sample path for black/whitelist files from /var/mail (which is meant to
be for mailboxes) to /etc/mail. Fritjof Bornebusch reported that security(8)
complains about files in /var/mail and suggested a subdirectory, but /etc
seems a better idea all-round, and matches hier(7).  ok jmc@