[feature/ajax] JavaScript strict mode

PHPBB3-10270

phpBB/adm/style/ajax.js

@@ -1,5 +1,6 @@
 (function($) {  // Avoid conflicts with other libraries
 
+"use strict";
 
 /**
  * The following callbacks are  for reording forums in acp_forums. forum_down

phpBB/assets/javascript/core.js

@@ -3,6 +3,8 @@ phpbb.alert_time = 100;
 
 (function($) {  // Avoid conflicts with other libraries
 
+"use strict";
+
 // define a couple constants for keydown functions.
 var keymap = {
 	ENTER: 13,

phpBB/styles/prosilver/template/ajax.js

@@ -1,5 +1,6 @@
 (function($) {  // Avoid conflicts with other libraries
 
+"use strict";
 
 // This callback finds the post from the delete link, and removes it.
 phpbb.add_ajax_callback('post_delete', function() {