Add debug mode for verbose logging

git-svn-id: https://plugins.svn.wordpress.org/duo-wordpress/trunk@879549 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fix an issue that caused 503 errors for some users running SSL sites

git-svn-id: https://plugins.svn.wordpress.org/duo-wordpress/trunk@879551 b8457f37-d9ea-0310-8a92-e5e31aec5664