Support this object being stored in the _class named attribute.

[proofit404]

class Container(Injector):
    foo = Foo
    foo_class = this.foo # error (class-named attribute point to non class-named attribute)

class Container(Injector):
    foo_class = Foo
    foo = this.foo_class # error (non class-named attribute point to class-named attribute)

class Container(Injector):
    foo = Foo
    bar = this.foo # ok

class Container(Injector):
    foo_class = Foo
    bar_class = this.foo_class # ok