#16 access to Session::checkSessionTime

[Jonathan Wakely]

when an application gets the onLogout() callback from Session::disconnect() there is no obvious way for the application to tell if the disconnection was because the session reached its configured EndTime, or if the session disconnected unexpectedly.

this makes it difficult for the application to know whether the logout was expected or is exceptional and should be logged or trigger an alert of some kind.

the application could ignore expected logouts if it could detect them e.g. if Session::enabled() returned false or if Session::checkSessionTime() was public