Fix some issues, add RPL_WHOISACCOUNT

irc/client.go

 	timestamp := client.resumeDetails.Timestamp
 	var timestampString string
 	if timestamp != nil {
-		timestampString := timestamp.UTC().Format("2006-01-02T15:04:05.999Z")
+		timestampString = timestamp.UTC().Format("2006-01-02T15:04:05.999Z")
 	}
 
-	oldClient := server.clients.Get(oldnick)
+	// can't use server.clients.Get since we hold server.clients' tier 1 mutex
+	casefoldedName, err := CasefoldName(oldnick)
+	if err != nil {
+		client.Send(nil, server.name, ERR_CANNOT_RESUME, oldnick, "Cannot resume connection, old client not found")
+		return
+	}
+
+	oldClient := server.clients.byNick[casefoldedName]
 	if oldClient == nil {
 		client.Send(nil, server.name, ERR_CANNOT_RESUME, oldnick, "Cannot resume connection, old client not found")
 		return

irc/numerics.go

 	RPL_CHANNELMODEIS               = "324"
 	RPL_UNIQOPIS                    = "325"
 	RPL_CHANNELCREATED              = "329"
+	RPL_WHOISACCOUNT                = "330"
 	RPL_NOTOPIC                     = "331"
 	RPL_TOPIC                       = "332"
 	RPL_TOPICTIME                   = "333"

irc/server.go

 	if target.flags[TLS] {
 		client.Send(nil, client.server.name, RPL_WHOISSECURE, client.nick, target.nick, "is using a secure connection")
 	}
+	accountName := target.AccountName()
+	if accountName != "" {
+		client.Send(nil, client.server.name, RPL_WHOISACCOUNT, client.nick, accountName, "is logged in as")
+	}
 	if target.flags[Bot] {
 		client.Send(nil, client.server.name, RPL_WHOISBOT, client.nick, target.nick, ircfmt.Unescape("is a $bBot$b on ")+client.server.networkName)
 	}
 
 	var timestamp *time.Time
 	if 1 < len(msg.Params) {
-		timestamp, err = time.Parse("2006-01-02T15:04:05.999Z", msg.Params[1])
-		if err != nil {
+		ts, err := time.Parse("2006-01-02T15:04:05.999Z", msg.Params[1])
+		if err == nil {
+			timestamp = &ts
+		} else {
 			client.Send(nil, server.name, ERR_CANNOT_RESUME, oldnick, "Timestamp is not in 2006-01-02T15:04:05.999Z format, ignoring it")
 		}
 	}
 		Timestamp: timestamp,
 	}
 
-	return true
+	return false
 }
 
 // USERHOST <nickname> [<nickname> <nickname> ...]