Close#7979.
This commit adds a much more usable whois tool compared to the ones in
busybox and inetutils.
The sources for whois and mkpasswd from Debian are both located in the whois
git repository for historical reasons.
The previous version (5.0.26) has been removed from the debian ftp.
As the source URL is now down, our own hydra (not hydra.nixos.org) failed
to build the package.
This problem will occur again in the future since I only updated the URL
without relying on a "more stable" alternative (this merits a specific
discussion).
