Commented Issue: Basic authentication does not work with POST & producer_consumer_buffer [22]

Version 1.1.0
Platform: Windows 7 client, VS2010, Windows 2008R2 server. IIS, ASP.NET

If I use basic authentication and POST with an istream body based on a producer_consumer_buffer, I get response 401. See sample code below.

If I switch to anonymous / no authentication, it works fine.
Or if I switch to setting the body as a vector<unsigned char> then it also works fine.

I would very much like to be able to stream the upload and use authentication together.

Regards,

David.

```

http_client_config config;
config.set_credentials(credentials(L"user",L"password"));

http_client client(U("http://localhost/test.ashx"), config);

http_request request(methods::POST);

producer_consumer_buffer<uint8_t> buff;

// Fill buff;

request.set_body(buff.create_istream());

auto response = client.request(request).get();
```
Comments: Hi David, I just wanted to let you know we haven't forgotten about this issue. It has turned out to be more difficult to fix than we initially thought, but we are still working on it. Steve