several security fixes in admin pages

changed bbcode to only allow jpg, jpeg, gif and png


git-svn-id: file:///svn/phpbb/branches/phpBB-2_0_0@4876 89ea8834-ac86-4346-8a33-228a782c2dd0

phpBB/admin/admin_ug_auth.php

@@ -56,6 +56,8 @@ while( list($var, $param) = @each($params) )
 
 $user_id = intval($user_id);
 $group_id = intval($group_id);
+$adv = intval($adv);
+$mode = htmlspecialchars($mode);
 
 //
 // Start program - define vars