Session never expires

This patch sends updated session cookies to the browser when the session is
refreshed on the server. This allows the session cookie to expire on the
browser at the same time the session timeout occurs at the server. In the
event the session timeout is configured in osTicket not to expire, the
cookie will expire after seven days on the client browser, and will expire
in PHP when it is garbage collected sometime after 86400 seconds after the
time last refresh time.

Using this method, the session will never expire if the session timeout in
osTicket is configured to 0, and the session is refreshed at least daily.