verify that expected changes have been made

[jelmer]

lintian is run as part of the package build step; the janitor should verify that those issues that were reported as fixed by lintian-brush no longer show up in the lintian output when building the package, and that no new lintian issues show up.

Ideally this would be done in a way that is not specific to lintian-brush changes, but can also be applied to e.g. multi-arch fixes or fresh upstreams.