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.