Comment 3 for bug 551510

I started work on this. As the 'trivial' tag indicates, it's fairly mechanical.

The only part I think is non-obvious is that the new apt_pkg.parse_depends and apt_pkg.parse_src_depends interfaces have a slight difference in how they return strictly-less and strictly-greater dependencies, indicating these by '<' and '>' rather than '<<' and '>>'. Personally I think this is a misdesign in apt; if you actually try to use '<' and '>' in control files you get less-or-equal and greater-or-equal semantics respectively due to a very old design error in dpkg, which is why we have '<<' and '>>' in the first place, and it's better not to confuse the situation further by exposing these as '<' and '>'. Thus, I think the right thing to do here is to map these operators back to the versions used in control files. There are only three relevant call sites so this isn't hard.