is_a() was deprecated briefly in PHP 5.3, switching to instanceof

Additionally, `instanceof` is a bit faster because it is a language construct and not a function! Woo!

Author: borkweb

WP_Router.class.php

@@ -221,7 +221,7 @@ protected function identify_route( $query ) {
 			return NULL;
 		}
 		$id = $query->query_vars[self::QUERY_VAR];
-		if ( !isset($this->routes[$id]) || !is_a($this->routes[$id], 'WP_Route') ) {
+		if ( !isset($this->routes[$id]) || ! $this->routes[$id] instanceof WP_Route ) {
 			return NULL;
 		}
 		return $id;