Documenation fixups for replication protocol.
There is no CopyResponse message; it should be CopyOutResponse.
Also, if there is no WAL to stream, the server does not immediately
send a CommandComplete; it's a historical timeline, so it will send a
response tuple first.
Discussion: https://postgr.es/m/
0a2c985ebcaa1acd385350aeba561b6509187394.camel@j-davis.com