So I created a single add_msg_ids() function (mostly migrated from postmsg.cpp)
to make this incredibly easy so any/everywhere that adds a message to a message
base should be able to call it. This function also creates reply-IDs (when
relevant) and program ID (Fido-PID) header fields:
- FIDOPID (always)
- FIDOMSGID (if an echomail post)
- FIDOREPLYID (if an echomail reply-post)
- RFC822MSGID (always)
- RFC822REPLYID (if a reply)