1) Change return from getCurrentValidations
2) Log tiebreaker logic to aid debugging
3) Change checkLastClosedLedger to use the new tie-breaker logic
4) Log when we refuse to switch to our own previous ledger
5) Track node ID in the serialized validation object
6) Simplify getCurrentValidations ledger suppression logic
closing time. Keep only the validation with the most recent signing time.
Sign using network time. This eliminates the ValidationPair nightmare and
makes the logic must easier to understand, increasing confidence that it
does what it's supposed to do.
