Switch http code header on showDebug with ErrorHTTPException.

app/FrontController.php

@@ -131,7 +131,11 @@ class FrontController
         } catch (Exception $e) {
             if (Config::get('DEBUG')) {
                 if (!headers_sent()) {
-                    header('HTTP/1.0 500 Internal Server Error');
+                    if ($e instanceof ErrorHTTPException) {
+                        header($e->getHTTPHeader());
+                    } else {
+                        header('HTTP/1.0 500 Internal Server Error');
+                    }
                 }
                 return ErrorHandler::showDebug($e);
             }