Nestmate same-package check

[Brian Goetz]

> The way I visualize this is that each newly arrived class
> checks in with its host.  If the name is on the list, it gets in.
>

Right, and if it's not on the list?  Does it get assigned its own 
nest-of-one, or do we reject the class?  I would expect the former? (If 
you show up at a party and you're not on the invite list, you can still 
have your own party, just not here.)