http://php.net/manual/en/function.session-set-save-handler.php:
When using objects as session save handlers, it is important
to register the shutdown function with PHP to avoid unexpected
side-effects from the way PHP internally destroys objects on
shutdown and may prevent the write and close from being called.
Typically you should register 'session_write_close' using the
register_shutdown_function() function.
We're not using objects as session save handlers, but some people
(notably, Synology users) seem to be encountering a similar issue
related to the timing of object destruction. Closing the session
earlier in the shutdown process is a perfectly sane thing to do, so
let's do it.
The table definition changed slightly and the old workaround didn't
work. If auth is disabled, we really don't care that much, so just drop
the attempt to constrain type in that case.
