Fix session migration upgrade crash

include/class.ostsession.php

@@ -135,7 +135,7 @@ abstract class SessionBackend {
     var $isnew = false;
     var $ttl;
 
-    function __construct($ttl) {
+    function __construct($ttl=SESSION_TTL) {
         $this->ttl = $ttl;
     }
 

include/upgrader/streams/core/c00511c7-7be60a84.task.php

@@ -6,7 +6,8 @@ class MigrateDbSession extends MigrationTask {
 
     function run() {
         # How about 'dis for a hack?
-        osTicketSession::write(session_id(), session_encode());
+        $session = new DbSessionBackend();
+        $session->write(session_id(), session_encode());
     }
 }