better unexpected error handling
check for add_filter function


git-svn-id: https://plugins.svn.wordpress.org/ag-custom-admin/trunk@863467 b8457f37-d9ea-0310-8a92-e5e31aec5664
1.3.4 version triggered

git-svn-id: https://plugins.svn.wordpress.org/ag-custom-admin/trunk@863470 b8457f37-d9ea-0310-8a92-e5e31aec5664