Merge branch 'bl/cherry-pick-empty'

Merge branch 'bl/cherry-pick-empty'

Allow git-cherry-pick(1) to automatically drop redundant commits via
a new `--empty` option, similar to the `--empty` options for
git-rebase(1) and git-am(1). Includes a soft deprecation of
`--keep-redundant-commits` as well as some related docs changes and
sequencer code cleanup.

* bl/cherry-pick-empty:
  cherry-pick: add `--empty` for more robust redundant commit handling
  cherry-pick: enforce `--keep-redundant-commits` incompatibility
  sequencer: do not require `allow_empty` for redundant commit options
  sequencer: handle unborn branch with `--allow-empty`
  rebase: update `--empty=ask` to `--empty=stop`
  docs: clean up `--empty` formatting in git-rebase(1) and git-am(1)
  docs: address inaccurate `--empty` default with `--exec`