message: Be more paranoid about cleaning submodules.
diff: @@ -12,6 +12,7 @@ def checkout_pr(String repo, String pr) {
  }
  sh """
  cd ${dir}
  + git clean -xffd
  git fetch https://github.com/stan-dev/${repo} +refs/pull/${prNumber}/merge:refs/remotes/origin/pr/${prNumber}/merge
  git checkout refs/remotes/origin/pr/${prNumber}/merge
  """
  @@ -48,6 +49,7 @@ pipeline {
  steps {
  retry(3) { checkout scm }
  sh 'git clean -xffd'
  + sh 'make stan-revert'
  script {
  if (params.stan_pr != '') {
  checkout_pr("stan", params.stan_pr)
  