Fix for #9058 and #8941, environment setup of RAILS_RELATIVE_URL_ROOT wa...

Fix for #9058 and #8941, environment setup of RAILS_RELATIVE_URL_ROOT was actually never used.

Here is the output with the suggested fix:

````rails
Loading development environment (Rails 4.1.0.beta)
>> ENV['RAILS_RELATIVE_URL_ROOT']
=> "/tributos"
>> Rails.application.routes.url_helpers.users_path
=> "/tributos/users"
>>
````

I'm not comfortable with referring to the ENV this way, however, I was not sure what would be the best way, and if at all, to reference: 

https://github.com/rails/rails/blob/master/railties/lib/rails/application/configuration.rb#L41

Would appreciate further input on this.