MSC2716: Incremental existing history

Fix https://github.com/matrix-org/matrix-doc/blob/matthew/msc2716/proposals/2716-importing-history-into-existing-rooms.md

Author: Eric Eastwood

clientapi/routing/routing.go

@@ -210,6 +210,7 @@ func Setup(
 			return SendEvent(req, device, vars["roomID"], vars["eventType"], nil, nil, cfg, rsAPI, nil)
 		}),
 	).Methods(http.MethodPost, http.MethodOptions)
+	// asdf
 	r0mux.Handle("/rooms/{roomID}/send/{eventType}/{txnID}",
 		httputil.MakeAuthAPI("send_message", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
 			vars, err := httputil.URLDecodeMapValues(mux.Vars(req))