3.1 release

git-svn-id: https://plugins.svn.wordpress.org/delete-duplicate-posts/trunk@980243 b8457f37-d9ea-0310-8a92-e5e31aec5664
3.1 release with WP 4.0

git-svn-id: https://plugins.svn.wordpress.org/delete-duplicate-posts/trunk@980463 b8457f37-d9ea-0310-8a92-e5e31aec5664