[Checkers] Interned test cases

[Matt Papi]

> Incidentally, earlier this morning I added a new failing test case to the
> Interned checker.  It's generics-related, but is also related to the topic
> of method overriding that we discussed a couple weeks ago.  Maybe you (or
> someone else, but please coordinate) could have a look at it when you get a
> chance.

Don't forget that there's a framework test suite, though you have to use
a different annotation (see the other tests in tests/framework). It
doesn't matter much to me, but for the sake of organization it might be
better to use this suite instead of the one for interned.


I took a quick look at the failing test, and it seems to be because 
SimpleSubtypeRelation.isSubtype doesn't call asSuper(). Mahmood and I 
were talking recently about whether isSubtype() or its caller should use 
asSuper() (i.e., whether "uses asSuper()" should be part of the spec of 
isSubtype()) and I don't remember if we came up with a good answer. 
However, I'm going to have SimpleSubtypeRelation use asSuper() (like IGJ 
does) for now, and we can change it later if necessary.

- Matt