Disable for certain images

git-svn-id: https://plugins.svn.wordpress.org/gif-animation-preview/trunk@1035184 b8457f37-d9ea-0310-8a92-e5e31aec5664
fix grammar

git-svn-id: https://plugins.svn.wordpress.org/gif-animation-preview/trunk@1035186 b8457f37-d9ea-0310-8a92-e5e31aec5664