padrino/padrino-framework — pull request #1690 by namusyaka (2014-05-30 12:48:01+00:00)
Title: AbstractFormBuilder#fields_for should respect the builder of parent

Now:
```ruby
form_for(@user, '/register', builder: "AbstractFormBuilder") do |f|
f #=> AbstractFormBuilder
f.fields_for(:role_types, @user.role_types) do |field|
field #=> StandardFormBuilder
field.submit_block "Submit"
end
end
```
I'd expected this:
```ruby
form_for(@user, '/register', builder: "AbstractFormBuilder") do |f|
f #=> AbstractFormBuilder
f.fields_for(:role_types, @user.role_types) do |field|
field #=> AbstractFormBuilder
field.submit_block "Submit"
end
end
```