Made the plugin work in a symlinked folder

git-svn-id: https://plugins.svn.wordpress.org/attached-posts/trunk@823127 b8457f37-d9ea-0310-8a92-e5e31aec5664
changed required wp version to 3.4 or higher

git-svn-id: https://plugins.svn.wordpress.org/attached-posts/trunk@823138 b8457f37-d9ea-0310-8a92-e5e31aec5664