Allow Internet Archive's Wayback machine to get stuff from bits etc.

Generic rule needs not be so generic; cf. 0e30a230 (Ie24e847).
Despite the name this is not about private content and won't "expose"
any private content, e.g. http://board.wikimedia.org/robots.txt is empty
and private pages are private anyway.

Bug: 65464
Change-Id: Iad648cc1e8e03e73652e81a81328273b4b49969f