[MERGE][0.16] Allow new smart client to work with old (<= 0.15) smart servers.

[Andrew Bennetts]

Robert Collins wrote:
> Andrew Bennetts wrote:
[...]
> 
> Isn't
> 
> smart_protocol = protocol.SmartClientRequestProtocolOne(request)
> server_version = smart_protocol.query_version()
> if server_version != '2':
>     raise errors.NotBranchError(path=transport.base)
> 
> better?

Duh.  Indeed it is.

> Other than that,
> 
> +1

Thanks!

-Andrew.