You’re 19, in a foreign country, and standing on the doorstep of someone you don’t know. As soon as you ring the doorbell, that someone becomes your friend, tour guide and host for the next few days. All you can hope is that you accurately interpreted their online persona as a suitable stranger to live with. It may sound like the beginning of a Dateline special on overseas abductions, but it’s the experience Belmont junior Jill Barrett took in the spring of 2011 as a couch su