We now accept unfeasible updates when the source hasn't changed, just don't
update the route's timestamp.  This makes it more likely that we have
up-to-date information while still avoiding loops.

Triggered updates are no longer sent when a route gets better.

This slows down convergence a little, but reduces the amount of traffic.

Rely on periodic updates instead.

I'm supersticious.

This is no longer needed now that we use a constant kernel priority.