correct usage of wpdb::prepare and get site-ids with wp_get_sites

git-svn-id: https://plugins.svn.wordpress.org/get-all-pages-widget/trunk@931099 b8457f37-d9ea-0310-8a92-e5e31aec5664
updated readme with changelog

git-svn-id: https://plugins.svn.wordpress.org/get-all-pages-widget/trunk@931100 b8457f37-d9ea-0310-8a92-e5e31aec5664