Bug fix: missing wpt_pro_exists() check

git-svn-id: https://plugins.svn.wordpress.org/wp-to-twitter/trunk@977979 b8457f37-d9ea-0310-8a92-e5e31aec5664
Switch to 2.9.2

git-svn-id: https://plugins.svn.wordpress.org/wp-to-twitter/trunk@977985 b8457f37-d9ea-0310-8a92-e5e31aec5664