stream-clone: check the version of streaming clone supported by the client...
stream-clone: check the version of streaming clone supported by the client
Make the server refuse to produce streaming clone bundle, if the client
doesn't specify the stream=v2 capability.
This is in preparation to introduce stream=v3.
As far as I can tell, this capability was added at the same time as
support for bundle2-based streaming pulls was added, so I don't expect
clients to break. (the modern client doesn't break, at any rate)
