Servers sometimes get disconnected without any feedback

[csmith]

No idea how to reproduce, I had a debug client running for a week and it didn't happen.

[csmith]

It looks like a server issue. I'm connected to three servers and getting a PING/sending a PONG to each for days, then one just stops sending PINGs.

I think we need to start sending our own PINGs and drop the server if they don't respond. (And by 'we' I mean ktirc)