Recognize '__' as an identifier-safe scope resolution substitute

Asking the injector directly for an instance of a namespaced class works fine using `Foo::Bar` or `foo/bar`, but neither of these are valid in ruby identifiers. This makes asking for an instance of a namespaced class by naming the class as a parameter to `initialize()` impossible.

Since `classify()` normally collapses multiple adjacent underscores, it should be safe to repurpose `__` as an identifier-safe alternative to `/`, suitable for use in parameter names.