Playlists are video by default. props duck_

Merges [30422] to the 4.0 branch.

Built from https://develop.svn.wordpress.org/branches/4.0@30423


git-svn-id: http://core.svn.wordpress.org/branches/4.0@30418 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/media.php

@@ -1247,6 +1247,10 @@ function wp_playlist_shortcode( $attr ) {
 		$atts['orderby'] = 'none';
 	}
 
+	if ( $atts['type'] !== 'audio' ) {
+		$atts['type'] = 'video';
+	}
+
 	$args = array(
 		'post_status' => 'inherit',
 		'post_type' => 'attachment',