function _checkFileExtension(filename, extension) {
  if (!extension || extension === true || extension === 'true') {
    extension = '';
  }
  if (!filename) {
    filename = 'untitled';
  }
  var ext = '';
  // make sure the file will have a name, see if filename needs extension
  if (filename && filename.indexOf('.') > -1) {
    ext = filename.split('.').pop();
  }
  // append extension if it doesn't exist
  if (extension) {
    if (ext !== extension) {
      ext = extension;
      filename = filename + '.' + ext;
    }
  }
  return [filename, ext];
}
@module IO
@submodule Table
@requires core