[Checkers] Annotation defaults and declarative specification of type hierarchy

[Michael Ernst]

Mahmood-

> This is a very reasonable proposal for use of DefaultQualifier, and  
> should be doable easily.

Great.  I'll continue my case study when it is implemented.

> > (Speculation alert:  I wonder if it would be useful to have a  
> > @DisjointFrom
> > annotation as well as a @SubtypeOf annotation.
> I'll need to think about this for a bit.

OK.  Without a use case, it may not be worth implementing.

                    -Mike