Slow downloads with limited FPS

With a low cl_maxidlefps, Curl_Frame() is called slowly and therefore downloads are slow.

So when you have a pile of big pk3s to download and you want to do something else while waiting, it will then take forever.

With cl_maxidlefps 10 I get around 160 KiB/s per download, I guess curl fetches 16KB of data per call.