libchan.Pipe and spdy.Pipe have different return value order

[Stephen Day]

sdpy has (sender, receiver), whereas libchan has (receiver, sender). These should match and should probably follow (receiver, sender), similar to the io package (reader, writer).

[Derek McGowan]

Agreed receiver before sender, this was an artifact of a previous design which never got cleaned up. Will have to investigate who might be effected by it.