Be less rigid about the shape of type annotations in units

Closes #535

typed-racket-lib/typed-racket/base-env/unit-prims.rkt

@@ -327,13 +327,13 @@
        ;; The inserted lambda expression will be expanded to the internal
        ;; name of the variable being annotated, this internal name
        ;; can then be associated with the type annotation during typechecking
-       [(define-values () (colon-helper (: name:id type) rest ...))
+       [(define-values () (colon-helper (: name:id type ...) rest ...))
         (quasisyntax/loc stx
           (define-values ()
             #,(tr:unit:body-exp-def-type-property
                #`(#%expression
                   (begin (void (lambda () name))
-                         (colon-helper (: name type) rest ...)))
+                         (colon-helper (: name type ...) rest ...)))
                'def/type)))]
        [(define-values (name:id ...) rhs)
         (quasisyntax/loc stx

typed-racket-test/succeed/unit-non-prefix-annotation.rkt

@@ -0,0 +1,13 @@
+#lang typed/racket/base
+
+(require typed/racket/unit)
+
+(define-signature sig^
+  ([f : (Integer → Integer)]))
+
+(define-unit sig@
+  (import)
+  (export sig^)
+
+  (: f : Integer → Integer)
+  (define (f x) (+ 1 x)))