add desktopstream

darcs-hash:20090429122434-b2873-d4f60fc36fdb2e2578693eb2f6d604d9310a1cdf
session2.NotificationHandler: make sure unsubcribe_from_all does not raise

darcs-hash:20090429125543-b2873-2d906bf61aba79985db18e75510d802830b8e494