round 1 of follow-up for metadata (#2277)

* refactoring
* send an empty batch if necessary, as per spec
* don't broadcast no-op updates
* don't trim spaces before validating the key
* bump irctest to cover metadata
* replay existing metadata to reattaching always-on clients
* use canonicalized name everywhere
* use utils.SafeErrorParam in FAIL lines
* validate key names for sub
* fix error for METADATA CLEAR
* max-keys is enforced for channels as well
* remove unlimited configurations
* maintain the limit exactly without off-by-one cases
* add final channel registration check

irc/server.go

@@ -496,6 +496,9 @@ func (server *Server) playRegistrationBurst(session *Session) {
 	if !(rb.session.capabilities.Has(caps.ExtendedISupport) && rb.session.isupportSentPrereg) {
 		server.RplISupport(c, rb)
 	}
+	if session.capabilities.Has(caps.Metadata) && c.AlwaysOn() {
+		playMetadataList(rb, d.nick, d.nick, c.ListMetadata())
+	}
 	if d.account != "" && session.capabilities.Has(caps.Persistence) {
 		reportPersistenceStatus(c, rb, false)
 	}