Merge branch 'nd/ita-cleanup' into maint

Paths that have been told the index about with "add -N" are not
quite yet in the index, but a few commands behaved as if they
already are in a harmful way.

* nd/ita-cleanup:
  grep: make it clear i-t-a entries are ignored
  add and use a convenience macro ce_intent_to_add()
  blame: remove obsolete comment