Make it possible to use Forever Frame when requested.

This pull request resolves #1057

- Instead of failing due to window.EventSource is supported, a log message sent that better transport methods are available.

This affects when you are specifying transport methods as an option to hub.start, that failed earlier if SSE was supported.
    $.connection.hub.start({ transport: ['foreverFrame', 'longPolling'] }, function() {
        console.log('connection started!');
    });

This means that it will affects the prioritization if specified like above.