code: function repoIsClean (done) {
    proc.exec('git status -z', function (err, stdout) {
      if (!err) {
        var msg = stdout.toString().trim();
        if (msg && msg.length) {
          err = new Error('Please commit all changes generated by building');
        }
      }
      done(err);
    });
  }
docs: Check if repo is clean