add test coverage for ComparableGroup.consistent_with

[mscarey]

I don't understand why the self_factor.contradicts(other_factor) call didn't have a context param. And I don't exactly understand how the all_generic_factors_match method is needed. Adding the missing context param fixed the broken test test_consistent_factor_groups_with_context, but I don't understand why the all_generic_factors_match doesn't make the context param redundant.