When refs/remotes/gfi/master and refs/remotes/gfi/HEAD exist,
and the latter is a symref that points at the former, dwim_ref()
resolves string "gfi" to "refs/remotes/gfi/master" as expected,
but dwim_log() does not understand "gfi@{1.day}" and needs to be
told "gfi/master@{1.day}". This is confusing.