Go back to guessing instead of trying to try every bestParent change. Try to make guesses cause fewer flappy routes. Track the time each link was last tested, use either the least recently tested link or the node's test time when deciding how old our info about a node is. Move tryExistingNode out of the conditional chain in the janitor, to prevent it from being blocked during bootstrapping (when we're most vulnerable to blackholes anyway). Misc code cleanup.