Merge branch 'sa/replay-atomic-ref-updates' into jch

"git replay" (experimental) learned to perform ref updates itself
in a transaction by default, instead of emitting where each refs
should point at and leaving the actual update to another command.

* sa/replay-atomic-ref-updates:
  replay: add replay.refAction config option
  replay: make atomic ref updates the default behavior
  replay: use die_for_incompatible_opt2() for option validation