Refresh packaging for 5.2.0-1

Changes are pretty straightforward: refresh patches, update symbols file, backport a single patch from the upstream master branch.

The package builds fine using pbuilder and the lintian report in not any worse than it was before the changes.

I have found a bunch of issues I'd like to address, but I think it's a better idea to update to 5.2.0 first, and then post such improvements as smaller, independent MRs targeted at 5.2.0-2 separately, rather than collapsing everything together in a single series.