Adding support for multiple menu locations

git-svn-id: https://plugins.svn.wordpress.org/menu-override/trunk@822824 b8457f37-d9ea-0310-8a92-e5e31aec5664
minor fix to prevent php warning

git-svn-id: https://plugins.svn.wordpress.org/menu-override/trunk@822840 b8457f37-d9ea-0310-8a92-e5e31aec5664