adjust hash/c so that it always copies immutable hashes

before this commit it would copy them only when the weren't
already impersonated/chaperoned, leading to different
contract checking that can be confusing in that case

it did this because the chaperone-of? check wasn't general
enough to cope with copying always, but since commit
b05d07ad10 it now is

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

@@ -191,6 +191,51 @@
       (for ([(k v) (in-hash h)])
         (hash-ref k v))))
   
+  (test/spec-passed
+   'hash/c14
+   '(let ()
+      (define h (hash 1 #f))
+      (hash-set (contract (hash/c integer? boolean?) h 'pos 'neg)
+                1 "x")))
+  
+  (test/spec-passed/result
+   'hash/c15
+   '(let ()
+      (define h (hash 1 #f))
+      (chaperone-of? (contract (hash/c integer? boolean?) h 'pos 'neg)
+                     h))
+   #t)
+  
+  (test/spec-passed
+   'hash/c16
+   '(let ()
+      (define h (hash 1 #f))
+      (define c-h
+        (chaperone-hash
+         h
+         (λ (h k) (values k (λ (h k v) v)))
+         (λ (h k v) (values k v))
+         (λ (h k) k)
+         (λ (h k) k)))
+      (hash-set (contract (hash/c integer? boolean?) c-h 'pos 'neg)
+                1 "x")))
+  
+  (test/spec-passed/result
+   'hash/c17
+   '(let ()
+      (define h (hash 1 #f))
+      (define c-h
+        (chaperone-hash
+         h
+         (λ (h k) (values k (λ (h k v) v)))
+         (λ (h k v) (values k v))
+         (λ (h k) k)
+         (λ (h k) k)))
+      (chaperone-of? (contract (hash/c integer? boolean?) c-h 'pos 'neg)
+                     c-h))
+   #t)
+
+  
   (test/pos-blame
    'hash/dc1
    '(contract (hash/dc [d integer?] [r (d) (if (even? d) string? symbol?)])

racket/collects/racket/contract/private/hash.rkt

@@ -237,16 +237,11 @@
 (define (handle-the-hash val neg-party
                          pos-dom-proj neg-dom-proj mk-pos-rng-proj mk-neg-rng-proj
                          chaperone-or-impersonate-hash ctc blame)
-  (if (and (immutable? val) (not (chaperone? val)))
-      (let ([hash-maker
-             (cond
-               [(hash-equal? val) make-immutable-hash]
-               [(hash-eqv? val) make-immutable-hasheqv]
-               [(hash-eq? val) make-immutable-hasheq])])
-        (hash-maker
-         (for/list ([(k v) (in-hash val)])
-           (cons ((pos-dom-proj k) neg-party)
-                 (((mk-pos-rng-proj k) v) neg-party)))))
+  (if (immutable? val) 
+      (for/fold ([h val]) ([(k v) (in-hash val)])
+        (hash-set h
+                  ((pos-dom-proj k) neg-party)
+                  (((mk-pos-rng-proj k) v) neg-party)))
       (chaperone-or-impersonate-hash
        val
        (λ (h k)