Fix compatibility issue with WP-Engine

git-svn-id: https://plugins.svn.wordpress.org/duo-wordpress/trunk@793150 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fix compatibility issues with WordPress versions 3.0-3.2.

git-svn-id: https://plugins.svn.wordpress.org/duo-wordpress/trunk@793772 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fix style of Duo's Save Changes button on settings page

git-svn-id: https://plugins.svn.wordpress.org/duo-wordpress/trunk@795446 b8457f37-d9ea-0310-8a92-e5e31aec5664