Try to recover from select() returning an error.

Try to recover from select() returning an error.

If we get an error back from select(), it could be because one of the
filedescriptors is in a bad state. This shouldn't occur, but if it does,
just call all the registered I/O callbacks to have them check for errors.
Only quit the event loop if the error persists.

Also fix some I/O callbacks that didn't expect to be called when the
filedescriptor isn't signalled.