Disallow lost exceptions (W0150).

* Exceptions should be explicitly caught and handled.
Handle exceptions explicitly.
Merge pull request #718 from Renelvon/no_lost_exc

Disallow early return from finally blocks (W0150)
market: reduce coupling between market and DHT implementation.

* Also decrease coupling by removing the return value,
  since it is not used anywhere.
transport: Refactor turn transport.store

* Turn it into a pure wrapper around dht.iterativeStore
  to reduce maintenance cost for changes in DHT.