Push/Pop the PHP session in order to keep OC and DW separated.

Dear Martin,

I already had contacted by email concerning owncloud/dokuwiki integration. So here is a pull request from my side. At least in my setup with OC-5.0.13 this is needed to provied an SSO solution for an into-OC embedded DW instance, together with your DW oc-auth plugin. The idea of the patch is a push/pop strategy for PHP sessions.

Related to this pull-request is a "dokuwikiembed" OC-app. That one was inspired by the Roundcube-app, but avoids storing any password. The user authenticates at the time of its login with OC _and_ DW. The cookies returned by DW are then simply forwarded to the user's web-browser.

There is one caveat: my OC-DW-app authenticates with DW via XMLRPC, but there is no "logout" action defined (yet). Implementing such a method is fairly simple, but I still wait for any echo on the DW mailing list before publishing a patch.

Kind regards,

Claus