/*
 * Get the visibility of the playlist window.
 *
 * Examples:
 *   puts 'playlist window visible' if remote.playlist_visible?
 *   puts 'playlist window visible' if remote.pl_visible?
 *   puts 'playlist window visible' if remote.playlist?
 *   puts 'playlist window visible' if remote.pl?
 *
 */
static VALUE xr_is_pl(VALUE self) {