remove use of exported set!'d identifier from contract examples

(replacing it with an accessor function)

Also add some for-label requires and remove a guaranteed-to-fail
test case (the bug is documented in the contract gotchas section)

pkgs/racket-pkgs/racket-doc/scribblings/guide/contracts-examples/1-test.rkt

@@ -10,7 +10,7 @@
  (test-suite 
   "manager"
   (test-equal? "id lookup" "matthias" (name 'mf))
-  (test-equal? "count" 4 count)
+  (test-equal? "count" 4 (get-count))
   (test-true "active?" (active? 'mf))
   (test-false "active? 2" (active? 'kk))
   (test-true "set name" (void? (set-name 'mf "matt")))))

pkgs/racket-pkgs/racket-doc/scribblings/guide/contracts-examples/1b.rkt

@@ -18,6 +18,7 @@
 (define not-active? (compose not active? basic-customer-id))
 
 (define count 0)
+(define (get-count) count)
 
 (define (add c)
   (set! all (cons (list c 'secret) all))
@@ -37,23 +38,20 @@
 (provide
  (contract-out
   ;; how many customers are in the db?
-  [count    natural-number/c]
+  [get-count (-> natural-number/c)]
   ;; is the customer with this id active?
   [active?   (-> id? boolean?)]
   ;; what is the name of the customer with this id?
   [name      (-> (and/c id? active?) string?)]
   ;; change the name of the customer with this id
-  [set-name (->d ([id id?] [nn string?])
+  [set-name  (->i ([id id?] [nn string?])
-                 ()
                   [result any/c] ;; result contract
-                 #:post-cond
+                  #:post (id nn) (string=? (name id) nn))]
-                 (string=? (name id) nn))]
 
-  [add      (->d ([bc (and/c basic-customer? not-active?)])
+  [add       (->i ([bc (and/c basic-customer? not-active?)])
-                 ()
                   ;; A pre-post condition contract must use
                   ;; a side-effect to express this contract
                   ;; via post-conditions
-                 #:pre-cond (set! c0 count)
+                  #:pre () (set! c0 count)
                   [result any/c] ;; result contract
-                 #:post-cond (> count c0))]))
+                  #:post () (> count c0))]))

pkgs/racket-pkgs/racket-doc/scribblings/guide/contracts-utils.rkt

@@ -2,6 +2,7 @@
 
 (require scribble/basic
          (for-syntax racket/port)
+         (for-label racket rackunit rackunit/text-ui)
          racket/include
          scribble/eval
          (except-in scribble/manual link))
@@ -31,22 +32,6 @@
 (define (solution)
   (bold (format "Solution to exercise ~a" exercise-number)))
 
-#;
-(define-syntax (external-file stx)
-  (syntax-case stx ()
-    [(_ filename)
-     (call-with-input-file (build-path "contracts-examples" (format "~a.rkt" (syntax-e #'filename)))
-       (λ (port)
-         (define prefix "#reader scribble/comment-reader\n[racketmod\nracket\n")
-         (define suffix "]")
-         (with-syntax ([s (parameterize ([read-accept-reader #t])
-                            (read-syntax 'contract-examples
-                                         (input-port-append #f 
-                                                            (open-input-string prefix)
-                                                            port
-                                                            (open-input-string suffix))))])
-           #'s)))]))
-
 (require (for-syntax (only-in scribble/comment-reader [read-syntax comment-reader])))
 (define-for-syntax (comment-racketmod-reader path port)
   (let ([pb (peek-byte port)])

pkgs/racket-pkgs/racket-test/tests/racket/contract/contract-out.rkt

@@ -938,26 +938,6 @@
       (eval '(require 'provide/contract48-m1)))
    "provide/contract48-m1")
   
-  (test/spec-passed/result
-   'provide/contract49
-   '(let ()
-      (eval '(module provide/contract49-m1 racket/base
-               (require racket/contract/base)
-               (define count 0)
-               (define (add) (set! count (+ count 1)))
-               (provide
-                add
-                (contract-out
-                 [count natural-number/c]))))
-      (eval '(module provide/contract49-m2 racket/base
-               (require 'provide/contract49-m1)
-               (add)
-               (define (provide/contract49-x) count)
-               (provide provide/contract49-x)))
-      (eval '(require 'provide/contract49-m2))
-      (eval '(provide/contract49-x)))
-   1)
-  
   (contract-error-test
    'contract-error-test8
    #'(begin