EngineBuffer: silent exceptions in shutdown

darcs-hash:20081118075114-b2873-32e3ec2499648abe2cab9351d4c78f541fb774f4
added __str__ to SIPDisconnect class

darcs-hash:20081118075251-b2873-c8f9746d7506d4e35499d655b98ad8386d9d8c13