user manager, ability to open the user add form with url parameter

to prepare the Tour of 2.9 new features

admin/themes/default/template/user_list.tpl

@@ -895,7 +895,7 @@ span.infos, span.errors {background-image:none; padding:2px 5px; margin:0;border
   <span class="infos" style="display:none"></span>
 </p>
 
-<form id="addUserForm" style="display:none" method="post" name="add_user" action="{$F_ADD_ACTION}">
+<form id="addUserForm" style="{if !isset($show_add_user)}display:none{/if}" method="post" name="add_user" action="{$F_ADD_ACTION}">
   <fieldset class="with-border">
     <legend>{'Add a user'|@translate}</legend>
 

admin/user_list.php

@@ -135,6 +135,11 @@ $template->assign(
     )
   );
 
+if (isset($_GET['show_add_user']))
+{
+  $template->assign('show_add_user', true);
+}
+
 // Status options
 foreach (get_enums(USER_INFOS_TABLE, 'status') as $status)
 {