Add tests for nAry, all arities of eq, where and propOrDefault

- Add new tests for nAry that didn't have tests before.
- Add test for currying eq.
- Add tests for eq, where and propOrDefault with 0 args.
- Fix eq to throw with 0 args.
Merge pull request #311 from fson/test-arity

Add tests for nAry, eq, where and propOrDefault