test cases & contracts in define-type

[robby]

This is really two bugs:

- the contract seems to not have a name for the function (see "on #f" in error message)

- there is no expected value in the result (see "<no-expected-value>")

#lang planet plai/plai:1:16
(define-type t (c (n number?)))
(test (c 'not-a-number) (list 5))

;; =>

(exception (c 'not-a-number) "use broke the contract (-> number? c1?) on #f; expected <number?>, given: not-a-number" <no-expected-value> "at line 3")

[plai]

I will fix this when the contract api is stable again.