Make the socket accessible externally for debuggging

(imported from commit 8f78d09edc05f8eed5f1a2d87643bdd7b7d9bec6)

static/js/compose.js

@@ -355,6 +355,9 @@ function send_message_ajax(request, success) {
 }
 
 var socket = new Socket("/sockjs");
+// For debugging.  The socket will eventually move out of this file anyway.
+exports._socket = socket;
+
 function send_message_socket(request, success) {
     socket.send(request, success, function (type, resp) {
         var err_msg = "Error sending message";