Treat all flags of a package as interdependent.
There was an open bug that could cause conflict sets to be computed incorrectly if flags were involved in the conflict set. Incorrectly computed conflict sets can lead to the solver not finding solutions even though they actually exist. Because I decided that computing flag dependencies correctly is tricky and probably not worth the effort, we're now treating all flags (of a package) as mutually dependent. This means that if any flag choice ends up in a conflict set, then it's as if all flag choices (of the same package) are in that conflict set. This is potentially slower for packages having many flags, but it should at least be correct, because it's conservative.