accesslib:require_capability() revamp to check for USER->access

$USER->capabilities is deprecated.

lib/accesslib.php

@@ -661,7 +661,7 @@ function require_capability($capability, $context=NULL, $userid=NULL, $doanythin
 
 /// If the current user is not logged in, then make sure they are (if needed)
 
-    if (empty($userid) and empty($USER->capabilities)) {
+    if (is_null($userid) && !isset($USER->access)) {
         if ($context && ($context->contextlevel == CONTEXT_COURSE)) {
             require_login($context->instanceid);
         } else if ($context && ($context->contextlevel == CONTEXT_MODULE)) {