code: function(stage) {
        var fileStart = options.dir + '/' + stage;
        for (var ext in input) {
          if (grunt.file.exists(fileStart + '.' + ext)) {
            return true;
          }
        }
        return false;
      }
docs: /*
  Returns true if a stage exists, false otherwise.
  A stage exists if there is a .json or .json5 with its name in the <options.dir> directory.
  This function does NOT check that the file is readable.