check for breaks/conflicts since the last merge

[Christian Ehrhardt ]

We have the full version history and can check e.g. on a "merge finish" or at linting stage (not sure which stage would work better)

Check for:
- changes to Breaks/Replaces between old/debian -> new/debian
Check if
- Ubuntu happened to have versions with an ubuntu0 in between

If both are true that might cause us to introduce the same change "later" than Debian and needs these dependencies to be bumped to when we introduce it.

Lets report those things to the user as "please double check these cases".
We could even spew out the git commit IDs introducing the original change.

[Christian Ehrhardt  (paelzer)]

tags lint / merge / both - I'm not sure

[Christian Ehrhardt  (paelzer)]

Thanks to amurray who got me thinking about it!

[Robie Basak (racb)]

Good shout!