Merge branch 'jc/you-still-use-whatchanged'

Merge branch 'jc/you-still-use-whatchanged'

"git whatchanged" that is longer to type than "git log --raw"
which is its modern rough equivalent has outlived its usefulness
more than 10 years ago.  Plan to deprecate and remove it.

* jc/you-still-use-whatchanged:
  whatschanged: list it in BreakingChanges document
  whatchanged: remove when built with WITH_BREAKING_CHANGES
  whatchanged: require --i-still-use-this
  tests: prepare for a world without whatchanged
  doc: prepare for a world without whatchanged
  you-still-use-that??: help deprecating commands for removal