Merge branch 'pw/advise-rebase-skip'

The mechanism to prevent "git commit" from making an empty commit or amending during an interrupted cherry-pick was broken during the rewrite of "git rebase" in C, which has been corrected. * pw/advise-rebase-skip: commit: give correct advice for empty commit during a rebase commit: encapsulate determine_whence() for sequencer commit: use enum value for multiple cherry-picks sequencer: write CHERRY_PICK_HEAD for reword and edit cherry-pick: check commit error messages cherry-pick: add test for `--skip` advice in `git commit` t3404: use test_cmp_rev