Extension talk:HideCategorizedOrphans/Flow

I managed to do this on Mediawiki 1.22.2 patching includes/specials/SpecialLonelypages.php like this:

--- SpecialLonelypages.php.bk   2014-12-11 12:32:41.317347781 +0100
+++ SpecialLonelypages.php      2014-12-11 12:38:09.453218165 +0100
@@ -52,7 +52,7 @@
                return array(
                        'tables' => array(
                                'page', 'pagelinks',
-                               'templatelinks'
+                               'templatelinks', 'categorylinks'
                        ),
                        'fields' => array(
                                'namespace' => 'page_namespace',
@@ -63,7 +63,8 @@
                                'pl_namespace IS NULL',
                                'page_namespace' => MWNamespace::getContentNamespaces(),
                                'page_is_redirect' => 0,
-                               'tl_namespace IS NULL'
+                               'tl_namespace IS NULL',
+                               'cl_from IS NULL'
                        ),
                        'join_conds' => array(
                                'pagelinks' => array(
@@ -77,7 +78,13 @@
                                                'tl_namespace = page_namespace',
                                                'tl_title = page_title'
                                        )
+                               ),
+                               'categorylinks' => array(
+                                       'LEFT JOIN', array(
+                                               'cl_from = page_id'
+                                       )
                                )
+
                        )
                );
        }

Hmm, so I'm trying to understand what this addition does? Its adding something with the categorylinks, but I don't understand what it means.