builtin-am: implement --rebasing mode
Since
3041c32 (am: --rebasing, 2008-03-04), git-am.sh supported the
--rebasing option, which is used internally by git-rebase to tell git-am
that it is being used for its purpose. It would create the empty file
$state_dir/rebasing to help "completion" scripts tell if the ongoing
operation is am or rebase.
As of
0fbb95d (am: don't call mailinfo if $rebasing, 2012-06-26),
--rebasing also implies --3way as well.
Since
a1549e1 (am: return control to caller, for housekeeping,
2013-05-12), git-am.sh would only clean up the state directory when it
is not --rebasing, instead deferring cleanup to git-rebase.sh.
Re-implement the above in builtin/am.c.
Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>