Publish status: hidden unless Auth

[fluffy-critter]

It'd be very useful to have a publish status that allows an item to be read by anyone but only appears on indexes for people on the auth list. So for example, if something is set as:

Status: XYZZY
Auth: friends

Anyone can see the entry itself with the URL, but only people on the friends list will see it in feeds or sequential navigation.

This would be useful for having semi-private entries which can be pointed to in side channels but which are also visible by default to trusted individuals.

However these entries should not appear in view.unauthorized since that would defeat the purpose (since that's typically used for providing a conditional "stub" entry to people who aren't logged in and for POSSE targets).