Convert the test suit to RSpec

Because of issues with Minitest and various versions of Rails, as well as the fact that we just don't use test/unit anymore, I've decided to convert the test suite to RSpec. This is a "90%" conversion, where most of the assertions remain, have been implemented via RSpec matchers, and live in `spec/support/assertions.rb`.

Also, since we touched this code, the hashes have been converted to 1.9 syntax where applicable.