Ensure that the downloads directory for CSV export exists

This will exist under normal operation, but when running tests
it will need to be created.
Test that CSV is returned by PublicBodyController.list_all_csv

This currently fails on Ruby 1.9
Use CSV instead of FasterCSV to fix an error under Ruby 1.9

If you use FasterCSV under Ruby 1.9 you get the NotImplementedError:

   Please switch to Ruby 1.9's standard CSV library.
   It's FasterCSV plus support for Ruby 1.9's m17n encoding engine.

This seems to still work fine under 1.8.7, so make that switch.