Be less clever about avoiding work.

We used to try to keep track of which routers had updates pending so
when new updates came in we could avoid growing the work queue with
trials for the router that would never be processed. This, it turns out,
is a Bad Idea. Don't do it.

Change-Id: Ia078953e9dfa548230c119ffb540a72152711112
Merge pull request #104 from dhellmann/debug-update-silent-failure

Be less clever about avoiding work.