New API: grpc.CancelClientStream(ClientStream)

[dfawley]

The only way to cancel a stream before the deadline expires today is via context cancelation. This process is asynchronous, but it is often desirable to have a synchronous way of cancelling an RPC such that users can be sure the stream has been closed before regaining control.

Implementing this feature would be done by:

1. Calling clientStream.cancel() (as the user would do)
2. Blocking until clientStream.finish() has finished (it will be called via the goroutine monitoring this context).