Christian Couder authored Jul 19, 2014 and Junio C Hamano committed Jul 21, 2014

When using --graft, with a mergetag in the original
commit, we should check that the commit pointed to by
the mergetag is still a parent of then new commit we
create, otherwise the mergetag could be misleading.

If the commit pointed to by the mergetag is no more
a parent of the new commit, we could remove the
mergetag, but in this case there is a good chance
that the title or other elements of the commit might
also be misleading. So let's just error out and
suggest to use --edit instead on the commit.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>