[Checkers] QualifierRoot Follow-up

[Mahmood Ali]

Hi,

> I propose to create a special annotations in the framework
> @Unqualified to be indicate that a qualifier is a subtype of
> unqualified type.  What do you think?

I implemented this approach but didn't check it in.  I should say that  
it was a bit annoying to go through the custom qualifiers (e.g. Odd,  
Encrypted, EncryptedPoly, etc.) and add SubtypeOf({Unqualified.class}).

It forces checker writers to include this line in all annotations,  
especially once meant for BasicChecker which are usually a subtype of  
unqualified (like the mentioned above).  I guess we can special case  
BasicChecker.

Regards,
Mahmood