Fix crash when linking. This requires a certain sequence of events: first a server is linked in successfully, then we need to REHASH, and then a new link attempt has to come in with the same server name (for example because there is a network issue and the old link has not timed out yet). If all that happens, then an UnrealIRCd 6 server may crash, but not always.
Two IRCv3 specifications were ratified which we already supported as drafts:
Change CAP draft/extended-monitor to extended-monitor
Add message-tag bot next to existing (for now) draft/bot