message: Remove the access token for the old IS
  Pretty important that we don't send that to the new IS...
diff: @@ -137,6 +137,7 @@ export default class SetIdServer extends React.Component {
  let newFormValue = this.state.idServer;
  if (!errStr) {
  MatrixClientPeg.get().setIdentityServerUrl(fullUrl);
  + localStorage.removeItem("mx_is_access_token", fullUrl);
  localStorage.setItem("mx_is_url", fullUrl);
  newFormValue = '';
  }
  