Merge branch 'al/bisect-first-parent'

Merge branch 'al/bisect-first-parent'

"git bisect" learns the "--first-parent" option to find the first
breakage along the first-parent chain.

* al/bisect-first-parent:
  bisect: combine args passed to find_bisection()
  bisect: introduce first-parent flag
  cmd_bisect__helper: defer parsing no-checkout flag
  rev-list: allow bisect and first-parent flags
  t6030: modernize "git bisect run" tests