swift234

Teach each archetype type to keep track of its nested types, so that
type substitution for a nested type reference (Foo.Bar.Wibble) whose
substituted parent reference (Foo.Bar) yields an archetype can simply
look for the appropriate nested type in the archetype. 

This allows us to eliminate the hideous ASTContext::AssociatedTypeMap
and simply the archetype builder.


Swift SVN r2438