t2202: make sure "git add" (no args) stays a no-op

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'jc/simple-add-must-be-a-no-op' into next

* jc/simple-add-must-be-a-no-op:
  t2202: make sure "git add" (no args) stays a no-op