Synchronized old 0.8 branch with master and Kafka 0.8.0-beta1

What this contains:

- Updated Kafka reference to 0.8.0-beta1 commit (looks dirty but it works)
- Disabled tests using commit offset to kafka (not available in 0.8, maybe in trunk)
- Updated doc, Kafka now requires calling `./sbt assembly-package-dependency`
- Updated tests & fixtures
- Moved integration test for blocking api in a different test function as it was causing me trouble. Makes more sense to have it split as well.

Integration tests work, _on my machine_. I used both tox (with pytest) and nosetests directly (which I prefer to pytest), not tested on 2.6 though.

@mahendra, @mumrah mrtheb/kafka-python@2b016b690d71e6c22656d214d7e951d82d7bb005 is for a fix you probably want in master as well.