function JSONPPolling(socket) {
            io.Transport['xhr-polling'].apply(this, arguments);

            this.index = io.j.length;

            var self = this;

            io.j.push(function(msg) {
                self._(msg);
            });
        }
The JSONP transport creates an persistent connection by dynamically
inserting a script tag in the page. This script tag will receive the
information of the Socket.IO server. When new information is received
it creates a new script tag for the new data stream.

@constructor
@extends {io.Transport.xhr-polling}
@api public