Merge branch 'pw/rebase-i-after-failure'

Merge branch 'pw/rebase-i-after-failure'

Various fixes to the behaviour of "rebase -i" when the command got
interrupted by conflicting changes.

* pw/rebase-i-after-failure:
  rebase -i: fix adding failed command to the todo list
  rebase --continue: refuse to commit after failed command
  rebase: fix rewritten list for failed pick
  sequencer: factor out part of pick_commits()
  sequencer: use rebase_path_message()
  rebase -i: remove patch file after conflict resolution
  rebase -i: move unlink() calls