fix incorrect chathistory batch types

This was introduced in 38a6d17ee5

irc/channel.go

 		}
 	}
 
-	batchID := rb.StartNestedBatch(chname, "chathistory")
+	batchID := rb.StartNestedBatch("chathistory", chname)
 	defer rb.EndNestedBatch(batchID)
 
 	for _, item := range items {

irc/client.go

 	if target == "" {
 		target = nick
 	}
-	batchID = rb.StartNestedBatch(target, "chathistory")
+	batchID = rb.StartNestedBatch("chathistory", target)
 
 	isSelfMessage := func(item *history.Item) bool {
 		// XXX: Params[0] is the message target. if the source of this message is an in-memory