1. As was discussed, these definitions should go into src/include/libpq/pqcomm.h, not a new file.
I'm ambivalent, this is very easy to do.
2. I would prefer an underscore after PgMsg, like PqMsg_DescribeRequest, so it's easier to visually locate the start of the actual message name.
3. IMO, the names of the protocol messages in protocol.sgml are canonical. Your patch appends "Request" and "Response" in cases where that is not part of the actual name. Also, some messages are documented to go both ways, so this separation doesn't make sense strictly speaking. Please use the names as in protocol.sgml without augmenting them.
I've changed this a number of times. I do not mind changing it again, but can we reach a consensus ?
