Better rewrite rule flushing in `test_permalink_without_title()`.

This ensures that the test is not polluted by permalink structure changes in
earlier tests.

git-svn-id: https://develop.svn.wordpress.org/trunk@30529 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/post.php

@@ -446,7 +446,9 @@ class Tests_Post extends WP_UnitTestCase {
 		// might only fail if the post ID is greater than four characters
 
 		global $wp_rewrite;
+		$wp_rewrite->init();
 		$wp_rewrite->set_permalink_structure('/%year%/%monthnum%/%day%/%postname%/');
+		$wp_rewrite->flush_rules();
 
 		$post = array(
 			'post_author' => $this->author_id,