Code review comment for lp:~jameinel/bzr-builddeb/changelog-parser

This removes the guts of the Changelog parsing code that I brought in, and replaces it by just importing debian_bundle.changelog and having that do the parsing.

I don't really like depending on cl._blocks, but since import_dsc is doing so, I assumed that was the best we could do.

The tests all still pass, and the parsing is going to be as accurate as python-debian's parsing, which is what import_dsc uses anyway.