Introduce "git replay", a tool meant on the server side without
working tree to recreate a history.
* cc/git-replay:
replay: stop assuming replayed branches do not diverge
replay: add --contained to rebase contained branches
replay: add --advance or 'cherry-pick' mode
replay: use standard revision ranges
replay: make it a minimal server side command
replay: remove HEAD related sanity check
replay: remove progress and info output
replay: add an important FIXME comment about gpg signing
replay: change rev walking options
replay: introduce pick_regular_commit()
replay: die() instead of failing assert()
replay: start using parse_options API
replay: introduce new builtin
t6429: remove switching aspects of fast-rebase