Fields use in bug fix

There was a bug in the recently included feature (fc4140ce76ba76038d259ba70ad39591260bf3c6) use_in that restricts a field from appearing in list or detail views of a resource.

The full_dehydrate method takes a for_list flag that was not being set in list methods.

I fixed the problem and added a test for one of the cases (get_list).

I'am a newbie in oss contibutions (my first pull request) so feel free to correct me in anything.