rails/rails — pull request #12510 by agios (2013-10-13 13:53:30+00:00)
Title: ActiveSupport::Inflector.underscore messes up acronyms under namespaces

For example:

```ruby
ActiveSupport::Inflector.inflections do |inflect|
inflect.acronym 'ISP'
inflect.acronym 'ISPs'
end

"ISP".pluralize.underscore
=> "isps" (ok)
"SomeISP".pluralize.underscore
=> "some_isps" (ok)
"Provider::ISP".pluralize.underscore
=> "provider/is_ps" (should be provider/isps)
```