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Now, all peers should be retrieved from the Peerstore, which will
construct the peers accordingly. This ensures there's only one peer
object per peer (opposite would be bad: things get out sync)

cc @whyrusleeping

Otherwise don't have the peer's target address.

- use log.* instead of u.*
- use automatic type conversions to .String()
  (Peer.String() prints nicely, and avoids calling b58 encoding
  until needed)

@perfmode boom

this will later have persistent storage, but no need yet

`v.([]byte)` coming from a datastore can panic.
`byt, ok := v.([]byte)` to be safe.

@whyrusleeping

it'll have to change lots since the listener is gone