In PHP 5.0.0, is_a() became deprecated in favour of the instanceof operator. Calling is_a() would result in an E_STRICT warning.

In PHP 5.3.0, `is_a()` is no longer deprecated, and will therefore no longer throw `E_STRICT` warnings.

To avoid warnings in PHP < 5.3.0, convert all `is_a()` calls to `$var instanceof WP_Class` calls.

`instanceof` does not throw any error if the variable being tested is not an object, it simply returns `false`.

Props markoheijnen, wonderboymusic.
Fixes #25672.

Built from https://develop.svn.wordpress.org/trunk@31188


git-svn-id: http://core.svn.wordpress.org/trunk@31169 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-feed.php

@@ -37,8 +37,9 @@ class WP_Feed_Cache_Transient {
 	}
 
 	public function save($data) {
-		if ( is_a($data, 'SimplePie') )
+		if ( $data instanceof SimplePie ) {
 			$data = $data->data;
+		}
 
 		set_transient($this->name, $data, $this->lifetime);
 		set_transient($this->mod_name, time(), $this->lifetime);