next: print some message when on a head with some aspiring children Being on a head does not necessary means that this is the end of the road. It is likely that some changesets could be evolve as children. We detect this case and provide a hint.

next: reword error output We move to a more compact and direct phrasing. I'm not fully happy about it yet, but this is a step forward. The listing of candidate should maybe be moved behind a --verbose flag (and such verbose flag be suggested in the error). G: changed tests/test-prev-next.t