Merge branch 'pw/rebase-i-author-script-fix'

Recent "git rebase -i" update started to write bogusly formatted
author-script, with a matching broken reading code.  These are
fixed.

* pw/rebase-i-author-script-fix:
  sequencer: fix quoting in write_author_script
  sequencer: handle errors from read_author_ident()

diff --cc sequencer.c
Simple merge

diff --cc t/t3404-rebase-interactive.sh
Simple merge