I'm not a skilled UI designer, so I suspect there may be even better
options, but it's definitely already better than the raw ASCII "---" we
had before.
Put the line only at the beginning because it looks bad if the line
after the label is misaligned when labels don't have the same width
(e.g. "Remote" vs. "Local" in the divergence view).
This test is interesting because it already behaves as desired: since git has
rescheduled the "pick" command, we do _not_ want to show a "conflict" entry in
this case, as we would see the same commit twice then.
