[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]))
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index 07815e8..019adad 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -10,7 +10,10 @@
 -  General Changes
 
    -  Added ``E_PARSE`` to the list of error levels detected by the shutdown handler.
-   -  Updated :doc:`Inflector Helper <helpers/inflector_helper>` function ``is_countable()`` with more words.
+   -  Updated :doc:`Inflector Helper <helpers/inflector_helper>` :php:func:`is_countable()` with more words.
+   -  Updated :doc:`common function <general/common_functions>` :php:func:`set_status_header()` with new status codes from IETF RFCs
+      `2817 https://tools.ietf.org/html/rfc2817>`_ (426)
+      and `6585 <https://tools.ietf.org/html/rfc6585>`_ (428, 429, 431, 511).
 
 Bug fixes for 3.1.1
 -------------------
@@ -40,7 +43,7 @@
 -  **Security**
 
    -  Fixed an SQL injection in the 'odbc' database driver.
-   -  Updated :php:func:`set_realpath()` :doc:`Path Helpr <helpers/path_helper>` function to filter-out ``php://`` wrapper inputs.
+   -  Updated :php:func:`set_realpath()` :doc:`Path Helper <helpers/path_helper>` function to filter-out ``php://`` wrapper inputs.
    -  Officially dropped any kind of support for PHP 5.2.x and anything under 5.3.7.
 
 -  General Changes