Modified MSRPStreamBase to stop other operations when an end is requested

Ignore-this: 1105180f6cc16bc5b60bdec9748f38fe

darcs-hash:20100111144247-1e3d8-fa8ba943260ab9cdd184161f6b8aae61e2cec6d6
Fixed race condition during ending of a SIP session

Ignore-this: 26fbf5d85a42fa9479f3392aef741626

darcs-hash:20100111161310-1e3d8-035a390349c573eb06031cd8a46bd070ba5b7fcf