swift234

Iterative type checker: satisfy dependencies of a request before the request.

Implement some awful, *recursive* code in the *iterative* type checker
that satisfies all of the dependencies of a type check request
(*recursively*) before satisfying the type check request itself. This
is placeholder code that lets us flesh out the dependency mechanism
separately from implementing the proper data structures.

To test this, implement a type check request for type-checking one
type within an inheritance clause. Make the superclass type check
request depend on the first type in the inheritance clause of the
class, with a recovery path that looks at subsequent types in the
inheritance clause so long as we're still seeing protocol types. This
checking is more minimal than what we were doing previously (where we
would check all of the inherited types to find the superclass) and a
simple illustration of dependencies that can evolve.

Swift SVN r32559