no-brainer patch for Active Support

I am revising AS stuff in the framework while covering core extension
for the AS guide.

There are class reopenings in Action Pack to add generic stuff like
TrueClass#to_param whose natural place would be AS/core_ext in my view
(where Array#to_param and friends live). Even Object#to_param is
defined twice.

I've refactored them out to standard places in AS, and added test
coverage which was lacking as well:

https://rails.lighthouseapp.com/projects/8994/tickets/2798

Totally +1.