magento/magento2 — pull request #556 by airbone42 (2014-04-22 09:14:54+00:00)
Title: Don't delete session data when regenerating ids on login

this would also remove the data of logged in user, so a login is actually not possible.

See the php manual for details on using session_regenerate_id: http://www.php.net/manual/en/function.session-regenerate-id.php