This commit converts the equivalent part of the shell script
`git-legacy-rebase.sh` to run the pre-rebase hook (unless disabled), and
to interrupt the rebase with error if the hook fails.
Signed-off-by: Pratik Karki <predatoramigo@gmail.com> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>