I should be able to show a "how to join" message on private Spaces

(User Story, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Bad Link: Thing 3y2868u not found, )
Security
Summary: That is, say I have a Space like the Carolingian Site Book. This is private, readable only by members, but if a non-member comes along, I want to be able to show a message saying how to request to join.
Pointed out by Chad.
This currently works for the Site Book, but it's a horrible hack. Implement this properly, and undo the hack.
Eventually, this should tie into the standard "Request to Join" mechanism, once that is in place. The design for this should be related to that, and they might want to be implemented together.