long-polling calls onMessagePublished in case of error

[xdenser]

this is strange
normally after call to
socket.push(data)
i do not get onMessagePublished
but if an error occurs during send in XMLHTTPRequest
then onMessagePublished is called and request object contains status "Ok"
error is in response body
actually nothing indicates clearly that there was some error
I would expect that the library either will retry to send the message or will call onError handler

to simulate just fail some of the requests in
XMLHTTPRequest.js
around
request = doRequest(options, responseHandler).on("error", errorHandler);