reflog: handle $name => remotes/%s/HEAD mapping consistently for logs

reflog: handle $name => remotes/%s/HEAD mapping consistently for logs

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.

Signed-off-by: Junio C Hamano <junkio@cox.net>