start-stop-start long polling results on a stream of poll requests

[NTaylorMullen]

Modify samples\Microsoft.AspNet.SignalR.Samples\Hubs\Test\chat.js to to this:

    hubConnection.start({ transport: activeTransport });
    hubConnection.stop();
    hubConnection.start({ transport: activeTransport });

On browser, open JS Console and connect to http://localhost:40476/hubs/test/chat.aspx?transport=longPolling

You will see infinite attempts to do a poll request
#2160

[halter73]

This issue was addressed by the following pull request:

#2600

[gustavo-armenta]

tested and there is only one pull request as expected