Selenide 3.9 introduced "new" way of downloading files using embedded proxy server.
It was described here: http://selenide.org/2016/09/03/selenide-3.9.2
It seems that many people have problems with the new mechanism. So let's disable it by default. Everyone who needs it can enable it via Configuration.fileDownload = PROXY;
Configuration.fileDownload = PROXY
Closes #402 Disable built-in proxy server by default