Fix opt-lambda:. Merge to 5.0.2.

(cherry picked from commit a15236ea4f)

collects/tests/typed-scheme/succeed/opt-lambda.rkt

@@ -0,0 +1,9 @@
+#lang typed/racket
+
+(: opt (case-lambda ( -> Void)
+                    (Integer -> Void)))
+(define opt
+  (opt-lambda: ((n : Integer 0))
+    (display n)))
+(opt)
+(opt 1)

collects/typed-scheme/private/prims.rkt

@@ -34,6 +34,7 @@ This file defines two sorts of primitives. All of them are provided into any mod
          "base-types.rkt"
          "base-types-extra.rkt"
          racket/flonum ; for for/flvector and for*/flvector
+         mzlib/etc
          (for-syntax 
           syntax/parse
 	  syntax/private/util