Do our own AutosaveInPlace operation.
Ensure that completion handlers are executed on the main queue.
Make sure that we set the modification date as the last thing.
Merge branch 'experimental/autosave-freeze-fix' into projects/scuttlebutt/master

* experimental/autosave-freeze-fix:
  Make sure that we set the modification date as the last thing.
  Ensure that completion handlers are executed on the main queue.
  Do our own AutosaveInPlace operation.