[Distutils] Declaring conflicts

[Thomas Lotze]

What's the recommended practice, if any, for declaring conflicts between
egg distributions? The use case I have in mind is changing dependencies
between packages A and B:

* A-1 depends on B-1, but not the other way around,
* I want to make B-2 depend on A-2, but not the other way around,
* and I want to make sure that if someone has A-1 and B-1 installed, they
  cannot upgrade only A, because A-2 and B-1 conflict in terms of
  functionality.

AFAICS, nothing prevents people from upgrading only A if only
dependencies, but no conflicts are declared. I didn't find any documented
way of declaring conflicts, though.

-- 
Thomas