add check to see if curl is installed

git-svn-id: https://plugins.svn.wordpress.org/feed-them-social/trunk@1003344 b8457f37-d9ea-0310-8a92-e5e31aec5664
add check to see if curl is installed

git-svn-id: https://plugins.svn.wordpress.org/feed-them-social/trunk@1003346 b8457f37-d9ea-0310-8a92-e5e31aec5664