Suppress test on Mac OS X

* test/automated/tramp-tests.el (tramp--test-darwin-p): New defun.
(tramp--test-utf8): Use it.

test/automated/tramp-tests.el

@@ -1772,6 +1772,14 @@ Several special characters do not work properly there."
       (file-truename tramp-test-temporary-file-directory) nil
     (string-match "^HP-UX" (tramp-get-connection-property v "uname" ""))))
 
+(defun tramp--test-darwin-p ()
+  "Check, whether the remote host runs Mac OS X.
+Several special characters do not work properly there."
+  ;; We must refill the cache.  `file-truename' does it.
+  (with-parsed-tramp-file-name
+      (file-truename tramp-test-temporary-file-directory) nil
+    (string-match "^Darwin" (tramp-get-connection-property v "uname" ""))))
+
 (defun tramp--test-check-files (&rest files)
   "Run a simple but comprehensive test over every file in FILES."
   ;; We must use `file-truename' for the temporary directory, because
@@ -2022,7 +2030,7 @@ Use the `ls' command."
 	(file-name-coding-system 'utf-8))
     (tramp--test-check-files
      (unless (tramp--test-hpux-p) "Γυρίστε το Γαλαξία με Ώτο Στοπ")
-     (unless (tramp--test-hpux-p)
+     (unless (or (tramp--test-hpux-p) (tramp--test-darwin-p))
        "أصبح بوسعك الآن تنزيل نسخة كاملة من موسوعة ويكيبيديا العربية لتصفحها بلا اتصال بالإنترنت")
      "银河系漫游指南系列"
      "Автостопом по гала́ктике")))