Some repositories might not use/have annotated tags (for example the
ones created with git-cvsimport) and git-submodule status might fail
because git-describe might fail to find a tag.  This change allows the
status of a submodule to be described/displayed relative to lightweight
tags as well.
Signed-off-by: NEmil Medve <Emilian.Medve@Freescale.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>