Show errors when hosts can't be polled

[xaprb]

I've verified with curl that the server:port collection shown in this screenshot all respond to GET /procs/, but they uncheck themselves silently. If John hadn't told me that means there's an error, I wouldn't have known it.

I would suggest to handle this a little differently: when there is such an error, not only uncheck that host, but also show a little div to the right of it, like this. Make it fade after 10s or so: