(Merge 3.4) Issue #19884, readline: calling rl_variable_bind

("enable-meta-key", "off") does crash on Mac OS X which uses libedit instead of
readline.

Modules/readline.c

@@ -1020,15 +1020,19 @@ setup_readline(readlinestate *mod_state)
     mod_state->begidx = PyLong_FromLong(0L);
     mod_state->endidx = PyLong_FromLong(0L);
 
+#ifndef __APPLE__
     if (!isatty(STDOUT_FILENO)) {
         /* Issue #19884: stdout is no a terminal. Disable meta modifier
            keys to not write the ANSI sequence "\033[1034h" into stdout. On
            terminals supporting 8 bit characters like TERM=xterm-256color
            (which is now the default Fedora since Fedora 18), the meta key is
            used to enable support of 8 bit characters (ANSI sequence
-           "\033[1034h"). */
+           "\033[1034h").
+
+           With libedit, this call makes readline() crash. */
         rl_variable_bind ("enable-meta-key", "off");
     }
+#endif
 
     /* Initialize (allows .inputrc to override)
      *