net/rpc: client's DialHTTPPath() treats http CONNECT response incorrectly

[AnimusPEXUS]

https://tools.ietf.org/html/rfc7231#section-4.3.6 - says: 'Any 2xx (Successful) response indicates that the sender (and all inbound proxies) will switch to tunnel mode immediately after the
blank line that concludes the successful response's header section;'

but DialHTTPPath() requires exactly resp.Status == "200 Connected to Go RPC"

https://github.com/golang/go/blob/master/src/net/rpc/client.go#L258
if err == nil && resp.Status == connected {
https://github.com/golang/go/blob/master/src/net/rpc/server.go#L688
var connected = "200 Connected to Go RPC"

[andybons]

@robpike