Test that #fresh_when accepts an array

This is simply a test case to prove that `#fresh_when` accepts an array of records. [etagger would raise an error](https://github.com/rails/etagger/pull/3) due to `#try`'s behavior in Rails 3 of raising an error if the method is not defined.

https://github.com/rails/etagger/pull/3

/cc @jeremy @rafaelfranca