deal with missing settings keys

git-svn-id: https://plugins.svn.wordpress.org/advertising-manager/trunk@1040811 b8457f37-d9ea-0310-8a92-e5e31aec5664
move split to preg_split

git-svn-id: https://plugins.svn.wordpress.org/advertising-manager/trunk@1040814 b8457f37-d9ea-0310-8a92-e5e31aec5664