evolve: support ancestor of orphan split with unrelated changeset in between This is done by searching for roots and heads within the range delimited on both sides by the target revs instead of just within the target revs. Example: o 5 | o 4 | o 3 | | * 2 | | | x 1 |/ o 0 1 is obsoleted by 3 and 5. We are considering the case when 2 gets evolved. Before the change, both roots and heads were [3, 5]. The user was offered a choice between 3 and 5 as the destination. After the change, roots are [3] and heads are [5]. 5 is chosen as the destination.