Use hash_equals() for old md5 hashes.

Merges [30412] to the 3.7 branch.

Built from https://develop.svn.wordpress.org/branches/3.7@30416


git-svn-id: http://core.svn.wordpress.org/branches/3.7@30411 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/pluggable.php

@@ -1492,7 +1492,7 @@ function wp_check_password($password, $hash, $user_id = '') {
 
 	// If the hash is still md5...
 	if ( strlen($hash) <= 32 ) {
-		$check = ( $hash == md5($password) );
+		$check = hash_equals( $hash, md5( $password ) );
 		if ( $check && $user_id ) {
 			// Rehash using new hash.
 			wp_set_password($password, $user_id);