* timeout connection already tracks "expected" responses
use this to deduplicate requests and do not ask a peer for the same thing again
(until either success or timeout)
* do not ask for orphan blocks repeatedly
allow more than preferred number of peers (clean if we exceed max number)
Moved handling to the peer map out of the p2p server and into
its own struct. Allowed factoring code from the net adapter and
simplification of some interactions. Also removes the need for
the adapter to reference the p2p server or peers.
Fixes#430, #453 and #456
