Need to be more careful when including base.php

Try to safe and restore some ini-parameters and disable session cookies
while including base.php
Also destroy the temporary oc session data
Do not destroy the session.

Actually, this partly conflicting session stuff between DokuWiki and
Owncloud need further investigation.
Finally fix the session stuff

Key was to change the session-id, of course, then destroy the dummy OC
session afterwards.