Reopen fileframe if it exists, fix 3.6 bug

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@766314 b8457f37-d9ea-0310-8a92-e5e31aec5664
Record generated image sizes so that WordPress can remove them when the media file is deleted

git-svn-id: https://plugins.svn.wordpress.org/ml-slider/trunk@766317 b8457f37-d9ea-0310-8a92-e5e31aec5664