rebase -i: fix post-rewrite hook with failed exec command

Usually, when 'git rebase' stops before completing the rebase, it is to give the user an opportunity to edit a commit (e.g. with the 'edit' command). In such cases, 'git rebase' leaves the sha1 of the commit being rewritten in "$state_dir"/stopped-sha, and subsequent 'git rebase --continue' will call the post-rewrite hook with this sha1 as <old-sha1> argument to the post-rewrite hook. The case of 'git rebase' stopping because of a failed 'exec' command is different: it gives the opportunity to the user to examine or fix the failure, but does not stop saying "here's a commit to edit, use --continue when you're done". So, there's no reason to call the post-rewrite hook for 'exec' commands. If the user did rewrite the commit, it would be with 'git commit --amend' which already called the post-rewrite hook. Fix the behavior to leave no stopped-sha file in case of failed exec command, and teach 'git rebase --continue' to skip record_in_rewritten if no stopped-sha file is found. Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr> Signed-off-by: Junio C Hamano <gitster@pobox.com>