Fixing caching issue collisions between controllers with the same names ...

...but different namespaces

The issue I've found recently is connected to the namespace usage. The app I develop has 2 sides API split for regular users and managers. And it's pretty straightforward that I have `UsersController` and `Manage::UsersController` for that purpose. Both of the controllers implement `index.json` method which is to be cached by `cache_all_output = true`. 

As you already might have guessed that lead to a collision of cache keys, thus I simply salted the cache key generation with a namespaced name of controller and it solved the issue.