In the following situation:

```ruby
class Bar
end

module Baz
end

class Foo
  prepend Baz
end

class Foo::Bar
end
```

Running `Inflector.constantize('Foo::Bar')` would blow up with a NameError.

What is happening is that `constatize` was written before the introduction
of prepend, and wrongly assume that `klass.ancestors.first == klass`.

So it uses `klass.ancestors.inject` without arguments, as a result
a prepended module is used in place of the actual class.