code: function initTmpDir (dirname, cb) {
    var dir = path.join(os.tmpDir(), dirname);
  
    rmrf(dir, function (err) {
      if (err) return cb(err);
      mkdir(dir, function (err) {
        if (err) return cb(err);
        cb(null, dir);
      });
    });
  }
docs: Initializes a tmp dir into which to place intermediate files
  
  @name initTmpDir
  @private
  @function
  @param {String} dirname
  @param {Function(Error, String)} cb called back with the full path to the initialized tmp dir