evolve: use more specific key name to store in evolvestate Now, as we also relocate divergent cset if required, so let's use more specific key to track the relocation of "divergent" and "other".

evolve: move a test where it makes more sense

evolve: remove the unnecessary condition to check empty successors set I annotated the history of this "newer == [()]" condition and found that it was added in the initial stages of evolution project (more than 8 years ago) and there is no test where we get [()] as a successor set. So looks like "if not newer" is enough to check if it is empty. I also looked into obsutil.successorssets() implementation and I don't think it would give us [()] in any case.