[ci skip] Add new HTTP status codes

https://tools.ietf.org/html/rfc2817
https://tools.ietf.org/html/rfc6585

Requested in #4835
diff --git a/system/core/Common.php b/system/core/Common.php
index 2c76519..257763d 100644
--- a/system/core/Common.php
+++ b/system/core/Common.php
@@ -544,13 +544,18 @@
 				416	=> 'Requested Range Not Satisfiable',
 				417	=> 'Expectation Failed',
 				422	=> 'Unprocessable Entity',
+				426	=> 'Upgrade Required',
+				428	=> 'Precondition Required',
+				429	=> 'Too Many Requests',
+				431	=> 'Request Header Fields Too Large',
 
 				500	=> 'Internal Server Error',
 				501	=> 'Not Implemented',
 				502	=> 'Bad Gateway',
 				503	=> 'Service Unavailable',
 				504	=> 'Gateway Timeout',
-				505	=> 'HTTP Version Not Supported'
+				505	=> 'HTTP Version Not Supported',
+				511	=> 'Network Authentication Required',
 			);
 
 			if (isset($stati[$code]))