Verify external cache are working properly

https://www.drupal.org/node/2364011

(worth also checking https://www.drupal.org/node/2364011#comment-9291895)
> Is there a use case for needing our own exit hook instead of the regular one?

It's the only way of running a hook whenever a request dispatched by RESTful is made. It will run for cached and uncached responses. It is interesting to do things like custom statistics of the API usage.

> Is there a use case for setting the cache variable, but not setting restful's page cache?

I think so. When Drupal is serving content and RESTful is exposing some other content you may want to cache one and not the other, depending on the nature of the content you're serving on each sub-system.

> why not use drupal_page_footer()?:

To be able to use out own `module_invoke_all('restful_exit')` and `variable_get('restful_page_cache', FALSE)`.