Merge branch 'dl/complete-rebase-and-archive'

The command line completion for "git archive" and "git rebase" are
now made less prone to go out of sync with the binary.

* dl/complete-rebase-and-archive:
  completion: teach archive to use __gitcomp_builtin
  completion: teach rebase to use __gitcomp_builtin

diff --cc contrib/completion/git-completion.bash
Simple merge