Different operating systems do behave quite differently when doing DNS
lookups, for example "127.0.0.1" sometimes resolves to "localhost" and
sometimes to "localhost.localdomain" (for example OpenBSD). And other
systems resolve "localhost" to the real host name (for example Cygwin).
So not using DNS at all makes the test site much more portable.
Some operating systems, for example OpenBSD, use "localhost.<domain>"
instead of "localhost", so the "who-test" expecting "localhost" failed
on such systems.
(Please see 149859c5fecc..., which fixes this for the who-test already)