Replacement stalled block logic. Depending on the situation, it will either disconnect
the peer (as previous behaviour), or it will reselect a syncnode (e.g. when 500 blocks
have been received from the syncnode).
Allow nodes to send version messages more than once.
Report ping times at they arrive.
Antisocial (needs CaughtUp)
Rename MarkBlockAsReceived to MarkBlockAsRequested to reduce confusion.
Force selection of a new syncnode since the current syncnode is about to stop sending blocks.
Only update last seen time when the node is actually being useful.
Add stats per node for tx and block uploads/downloads.
Remove tx from AlreadyAskedFor list once we receive it, not when we process it.
Add debug info for sending of invs
Log mempool requests
Change AskFor to remove kludge that was needed when time was stored in seconds.

Not needed now that time is stored in Milliseconds.