Don't display ‘’ as `' under X in en_GB

The curved quote setup code invokes (char-displayable-p ?‘),
but this isn’t reliable until after the X frame replaces the
terminal frame (Bug#20926).
* lisp/international/mule-cmds.el (set-locale-environment):
Move curved quote setup code from here ...
* lisp/startup.el (command-line): ... to here, after creating
the X frame.

lisp/international/mule-cmds.el

@@ -2731,14 +2731,6 @@ See also `locale-charset-language-names', `locale-language-names',
 	(set-terminal-coding-system 'utf-8)
 	(set-keyboard-coding-system 'utf-8)))
 
-    ;; If curved quotes don't work, display ASCII approximations.
-    (unless frame
-      (dolist (char-repl '((?‘ . [?\`]) (?’ . [?\']) (?“ . [?\"]) (?” . [?\"])))
-        (when (not (char-displayable-p (car char-repl)))
-          (or standard-display-table
-              (setq standard-display-table (make-display-table)))
-          (aset standard-display-table (car char-repl) (cdr char-repl)))))
-
     ;; Default to A4 paper if we're not in a C, POSIX or US locale.
     ;; (See comments in Flocale_info.)
     (unless frame

lisp/startup.el

@@ -1017,6 +1017,14 @@ please check its value")
 				'("no" "off" "false" "0")))))
     (setq no-blinking-cursor t))
 
+  ;; If curved quotes don't work, display ASCII approximations.
+  (unless noninteractive
+    (dolist (char-repl '((?‘ . [?\`]) (?’ . [?\']) (?“ . [?\"]) (?” . [?\"])))
+      (when (not (char-displayable-p (car char-repl)))
+        (or standard-display-table
+            (setq standard-display-table (make-display-table)))
+        (aset standard-display-table (car char-repl) (cdr char-repl)))))
+
   ;; Re-evaluate predefined variables whose initial value depends on
   ;; the runtime context.
   (mapc 'custom-reevaluate-setting