winhttp: Add support for WinHttpRequestOption_URLCodePage.

[Hans Leidekker]

On Mon, 2015-08-24 at 15:03 +0800, Dmitry Timoshkov wrote:
> @@ -3071,6 +3072,7 @@ static void initialize_request( struct winhttp_request *request )
>      request->connect_timeout = 60000;
>      request->send_timeout    = 30000;
>      request->receive_timeout = 30000;
> +    request->url_codepage = CP_ACP;

MSDN says that it defaults to CP_UTF8 and my tests confirm that.