Added one test to the polymorph suite (test name usage)

* added one tests that verifies that the diet function also
  accesses the name value of the map (before it was possible
  to just return "Bambi eats veggies." for the herbivore diet
* since this is not the main purpose of these specs added just
  this one and not extra specs for default/carnivore as I didn't
  want to bloat it, but could add those as well if desired
* tried to stick to the disney animals theme (kind of)

Just noticed this when going through the koans myself, thanks for them - they are a great learning tool!

Tobi