list: make permutations and in-permutations ordering agree

In `permutations`, we need to reverse the list, because we want to build
the list backward by consing the last element until the first element.
`in-permutations`, however, generates each element from front-to-back,
so we should not need reversing.

Also adjust existing tests so that it checks that both orders agree.

pkgs/racket-test-core/tests/racket/list.rktl

@@ -490,10 +490,10 @@
                           (and (= (car l1) (car l2))
                                (loop (cdr l1) (cdr l2)))))))
   (define (sorted-perms l)
-    (define l1 (sort (permutations l) perm<?))
-    (define l2 (sort (for/list ([p (in-permutations l)]) p) perm<?))
+    (define l1 (permutations l))
+    (define l2 (for/list ([p (in-permutations l)]) p))
     (test #t equal? l1 l2)
-    l1)
+    (sort l1 perm<?))
   (test '(())  sorted-perms '())
   (test '((1)) sorted-perms '(1))
   (test '((1 2) (2 1)) sorted-perms '(1 2))

racket/collects/racket/list.rkt

@@ -770,7 +770,7 @@
          (when (> N 254) (error 'permutations "input list too long: ~e" l))
          (define c (make-bytes (add1 N) 0))
          (define i 0)
-         (define cur (reverse l))
+         (define cur l)
          (define (next)
            (define r cur)
            (define ci (bytes-ref c i))