cron: Delete Expired Sessions

This addresses an issue where expired sessions would not be removed from
the database. This caused the session table to fill up and create
unnecessary issues. This adds a cleanup method to remove all expired
sessions from the database.

include/class.cron.php

@@ -51,6 +51,11 @@ class Cron {
         AttachmentFile::deleteOrphans();
     }
 
+    function CleanExpiredSessions() {
+        require_once(INCLUDE_DIR.'class.ostsession.php');
+        DbSessionBackend::cleanup();
+    }
+
     function MaybeOptimizeTables() {
         // Once a week on a 5-minute cron
         $chance = rand(1,2000);
@@ -100,6 +105,7 @@ class Cron {
         self::MailFetcher();
         self::TicketMonitor();
         self::PurgeLogs();
+        self::CleanExpiredSessions();
         // Run file purging about every 10 cron runs
         if (mt_rand(1, 9) == 4)
             self::CleanOrphanedFiles();

include/class.ostsession.php

@@ -158,6 +158,10 @@ abstract class SessionBackend {
         return $this->update($id, $i['touched'] ? session_encode() : $data);
     }
 
+    function cleanup() {
+        $this->gc(0);
+    }
+
     abstract function read($id);
     abstract function update($id, $data);
     abstract function destroy($id);
@@ -220,6 +224,10 @@ extends SessionBackend {
         return SessionData::objects()->filter(['session_id' => $id])->delete();
     }
 
+    function cleanup() {
+        self::gc(0);
+    }
+
     function gc($maxlife){
         SessionData::objects()->filter([
             'session_expire__lte' => SqlFunction::NOW()