Conform to pep8 rules.

/usr/local/bin/autopep8 --in-place --max-line-length=120 --ignore=E501 --jobs=0 --recursive --pep8-passes=3 .
Pep8 says 0L should be 0, hence the assert must allow int.
Merge pull request #55 from boudewijn-tribler/code-cleanup

Conform to pep8 rules.