Janitor stuff. For the nodeMill, require that nodes are in some way useful (e.g. needed for keyspace or are an unknown hop on someone's best path). Add checkPeers to dht maintenance.
Make checkPeers return a bool for if it did anything. Have tryExistingNode try checkPeers on the node before pinging it. Modify linkMill/nodeMill/tryRandomLink priorities, the mills now eventually empty.
return
Since the mills eventually empty, we can move the random node ping to after them. This should speed up bootstrapping and recovery after a disconnect, but have ~no effect once we reach a full maintenance state.
Store the time each node was last pinged successfully. Reset on path changes. Include it in dumptable. Added support for this in dumptable.js
Merge branch 'janitor' of https://github.com/Arceliar/cjdns into crashey