Fixed Session.end in case a media stream fails during its execution

Ignore-this: 7da573c324a45813d373fa8f6d33a18b

darcs-hash:20100106121049-1e3d8-e336c4f590c7e74f6bc2917302c1fde4b5288601
Removed old import

darcs-hash:20100106123132-58252-e72e631a7a8d9b6ce88b015c578fad0eb80317e2