Merge branch 'cc/cherry-pick-ff'

Merge branch 'cc/cherry-pick-ff'

* cc/cherry-pick-ff:
  revert: fix tiny memory leak in cherry-pick --ff
  rebase -i: use new --ff cherry-pick option
  Documentation: describe new cherry-pick --ff option
  cherry-pick: add tests for new --ff option
  revert: add --ff option to allow fast forward when cherry-picking
  builtin/merge: make checkout_fast_forward() non static
  parse-options: add parse_options_concat() to concat options