It's nice to see the result of "branch move", "create", etc., and this is more
important in "branch move" because the source branches can be specified in an
abstracted way. I originally considered printing a list of affected branches,
but it looked rather verbose. Since the destination revision is unique, we can
use commit_summary template instead.
This patch also removes a warning about multiple branches because the branch
names are included in the commit summary. I think the hint message is good
enough to signal possible mistake.
cdc0cc3601