add if exists around TwitterOAuth Class

git-svn-id: https://plugins.svn.wordpress.org/twitter-stream/trunk@878385 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update version number

git-svn-id: https://plugins.svn.wordpress.org/twitter-stream/trunk@878389 b8457f37-d9ea-0310-8a92-e5e31aec5664