Fix a hard-coded database table typo. s/wp_users/$wpdb->users/

git-svn-id: http://svn.automattic.com/wordpress/trunk@15702 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/user.php

@@ -416,7 +416,7 @@ class WP_User_Query {
 				FROM wp_posts
 				$where
 				GROUP BY post_author
-			) p ON (wp_users.ID = p.post_author)
+			) p ON ({$wpdb->users}.ID = p.post_author)
 			";
 			$orderby = 'post_count';
 		}