market: reduce coupling between market and DHT implementation.

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

* Turn it into a pure wrapper around dht.iterativeStore
  to reduce maintenance cost for changes in DHT.
an up to date changelog with the latest version number is necessary for the debian building tools. re-introducing changelog update lost on release-0.2.0 branch
fixes on ubuntu build folder that were breaking the build process.
Merge pull request #720 from Renelvon/decouple2

Decouple market implementation from DHT
Merge pull request #726 from gubatron/0.2.0-debian-builder-fixes

0.2.0 debian builder fixes
Flag implicit relative imports (W0403).
State relative imports explicitly.

* Reorder imports in accordance to PEP8.
* Replace calls to privtopub with calls to
  privkey_to_pubkey for consistency.