Release 5.2.21

git-svn-id: https://plugins.svn.wordpress.org/wp-photo-album-plus/trunk@879501 b8457f37-d9ea-0310-8a92-e5e31aec5664
Release 5.2.21 readme upd

git-svn-id: https://plugins.svn.wordpress.org/wp-photo-album-plus/trunk@879508 b8457f37-d9ea-0310-8a92-e5e31aec5664