evolve: add test to demonstrate a bug when no active topic Added test shows that the logic to find the destination for `hg up` in the case when "working directory parent has a topic but wdir has no active topic" is buggy. This will be fixed in next patch.

evolve: fix a bug in logic of choosing destination for hg update

evolve: add test to demonstrate a bug when active topic is empty Added test shows that when current active topic is empty and we try to run `hg up`, it fails with an error. It's because this case is not correctly handled when we find a destination to update (when topics are in play) Next patch will fix this.