Adds three more levels of privacy to the Options-->Privacy page. Drop into mu-plugins.

1. Blog visible to any logged in community member.

2. Blog visible only to registered users of blog.

3. Blog visible only to administrators.

UPDATE 2.0 all options redirect through login.php, securing blog feeds now, too.(site-wide feed???)

Update May/24/08: site admin can also set privacy at misc. blog actions in wpmu-blogs.php

Update 2.2 May 29/08 removed cookie checks causing infinite redirects in WPMU1.5.1

Update 2.3 July3/08 added check for logged in user fixing more infinite redirects in WPMU1.5.1

Update 2.5 July 9/08 More tweaks. Added a timed refresh/redirect message for logged in users in the same css as the login page.