Bug fix for SQLite cache string encoding/decoding on Python 3.x
Bug fix for check_package() on Python 3.x
Make collect_related_packages() a bit faster*

* Actually quite a lot when `dpkg --compare-versions' is being used :-)
Make deb_pkg_tools.control.* less verbose
Bug fix for obscure Python 3.x issue*

* Caused by mutating a list while iterating it.