add a test case for the contract system error (and adjust the fix a little bit)

collects/racket/contract/private/arrow.rkt

@@ -235,7 +235,7 @@ v4 todo:
                                      post ...
                                      rng-results]
                                     [args
-                                     (bad-number-of-results blame val rng-len (length args))]))))
+                                     (bad-number-of-results blame val rng-len args)]))))
                            null)])
           (let* ([min-method-arity (length doms)]
                  [max-method-arity (+ min-method-arity (length opt-doms))]
@@ -1863,7 +1863,8 @@ v4 todo:
     [else
      passes?]))
 
-(define (bad-number-of-results blame val rng-len num-values)
+(define (bad-number-of-results blame val rng-len args)
+  (define num-values (length args))
   (raise-blame-error blame val 
                      "expected ~a value~a, returned ~a value~a"
                      rng-len (if (= rng-len 1) "" "s")

collects/tests/racket/contract-test.rktl

@@ -886,6 +886,15 @@
                'neg)
      1))
 
+  (test/pos-blame
+   'contract-arrow-values5
+   '((contract (-> integer? (values integer? integer?))
+               (lambda (x) x)
+               'pos
+               'neg)
+     1))
+
+  
   (test/pos-blame
    'contract-arrow-keyword1
    '(contract (-> integer? any)