* 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