Through the years the functionality to handle @{-N} and @{u} has moved
around the code, and as a result, code that once made sense, doesn't any
more.
There is no need to call this function recursively with the branch of
@{-N} substituted because dwim_{ref,log} already replaces it.
However, there's one corner-case where @{-N} resolves to a detached
HEAD, in which case we wouldn't get any ref back.
So we parse the nth-prior manually, and deal with it depending on
whether it's a SHA-1, or a ref.
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>