evolve: support successors of ancestor of orphan with multiple roots The previous code checked that the set of successors has a single root. However, there’s no reason to require that in general. Example: o 6 | o 5 |\ | o 4 | | o | 3 |/ | * 2 | | | x 1 |/ o 0 1 is obsoleted by 3, 4 and 6. We are considering the case when 2 gets evolved. The roots are [3, 4] and the heads are [6]. Before the change, the user was asked which destination to choose, but there was only one choice (6). After the change, 6 is chosen as the destination.