Merge branch 'rs/add-dry-run-without-objects'

Stop "git add --dry-run" from creating new blob and tree objects.

* rs/add-dry-run-without-objects:
  add: don't write objects with --dry-run

t/t2200-add-update.sh

@@ -129,12 +129,15 @@ test_expect_success 'add -n -u should not add but just report' '
 		echo "remove '\''top'\''"
 	) >expect &&
 	before=$(git ls-files -s check top) &&
+	git count-objects -v >objects_before &&
 	echo changed >>check &&
 	rm -f top &&
 	git add -n -u >actual &&
 	after=$(git ls-files -s check top) &&
+	git count-objects -v >objects_after &&
 
 	test "$before" = "$after" &&
+	test_cmp objects_before objects_after &&
 	test_cmp expect actual
 
 '