Merge branch 'pw/rebase-i-internal'

Merge branch 'pw/rebase-i-internal'

The internal implementation of "git rebase -i" has been updated to
avoid forking a separate "rebase--interactive" process.

* pw/rebase-i-internal:
  rebase -i: run without forking rebase--interactive
  rebase: use a common action enum
  rebase -i: use struct rebase_options in do_interactive_rebase()
  rebase -i: use struct rebase_options to parse args
  rebase -i: use struct object_id for squash_onto
  rebase -i: use struct commit when parsing options
  rebase -i: remove duplication
  rebase -i: combine rebase--interactive.c with rebase.c
  rebase: use OPT_RERERE_AUTOUPDATE()
  rebase: rename write_basic_state()
  rebase: don't translate trace strings
  sequencer: always discard index after checkout