updated custom metaboxes class

git-svn-id: https://plugins.svn.wordpress.org/infinite-slider/trunk@969547 b8457f37-d9ea-0310-8a92-e5e31aec5664
updated custom metaboxes class

git-svn-id: https://plugins.svn.wordpress.org/infinite-slider/trunk@969548 b8457f37-d9ea-0310-8a92-e5e31aec5664