Add some missing MW version documentation

* deprecate $wgAuth
* add @since for Status::getStatusValue

Change-Id: Ia11ef1e4788297ffea0a2beb4da731c7e771958c

includes/DefaultSettings.php

@@ -7057,6 +7057,7 @@ $wgExtensionCredits = [];
 /**
  * Authentication plugin.
  * @var $wgAuth AuthPlugin
+ * @deprecated since 1.27 use $wgAuthManagerConfig instead
  */
 $wgAuth = null;
 

includes/Status.php

@@ -118,6 +118,7 @@ class Status {
 	/**
 	 * Returns the wrapped StatusValue object
 	 * @return StatusValue
+	 * @since 1.27
 	 */
 	public function getStatusValue() {
 		return $this->sv;