Updated JEP: nestmates

[Brian Goetz]

> The second part most certainly is necessary as a nest-top does not 
> itself have a nest-top!

I would think we'd consider a nest-top as its own nest-top. That way, 
every nest has a top, which acts as a canonical element for that nest.

> It is not an optimization! You are either a nest-top (and so have a 
> NestMembers attribute) or you are a nested type and so have a 
> MemberOfNest attribute. (Of course you can be neither.) 

Similarly, I'd think that every class that has neither a NestMembers or 
MemberOfNest attribute constitutes a nest of one.

Taken together, now:
  - Every class belongs to exactly one nest;
  - Every nest has a canonical, consistent nest-top (every member of the 
nest agrees on the nest top)

This will become relevant when we extend this to support 
Lookup.defineClass with a private lookup, which has the effect of 
injecting a new class into an existing nest.  If every class is already 
in a nest, this injection is simplified.