function yoast_bitly_shortlink($url, $id, $context, $allow_slugs) {
	if ( ( is_singular() && !is_preview() ) || $context == 'post' ) {
		$short = get_post_meta($id, '_yoast_bitlylink', true);
		if ( !$short || $short == '' ) {
			if ( !defined('BITLY_USERNAME') || !defined('BITLY_APIKEY') ) {
				$short = 'http://yoast.com/wordpress/bitly-shortlinks/configure-bitly/';
			} else {
				$url = get_permalink( $id );
				$resp = wp_remote_get('http://api.bit.ly/v3/shorten?format=txt&longUrl='.$url.'&login='.BITLY_USERNAME.'&apiKey='.BITLY_APIKEY);
				if (is_array($resp))
					if ( $resp['response']['code'] == 200 ) {
						$short = $resp['body'];
						update_post_meta( $id, '_yoast_bitlylink', $short);
					}
			}
		}
		return $short;
	}
	return false;
}
add_filter('pre_get_shortlink','yoast_bitly_shortlink',99,4);