Merge branch 'rs/p3400-lose-tac'

Test portability update.

* rs/p3400-lose-tac:
  p3400: stop using tac(1)

Author: gitster

t/perf/p3400-rebase.sh

@@ -18,7 +18,7 @@ test_expect_success 'setup rebasing on top of a lot of changes' '
 		test_tick &&
 		git commit -m commit$i unrelated-file$i &&
 		echo change$i >unrelated-file$i &&
-		test_seq 1000 | tac >>unrelated-file$i &&
+		test_seq 1000 | sort -nr >>unrelated-file$i &&
 		git add unrelated-file$i &&
 		test_tick &&
 		git commit -m commit$i-reverse unrelated-file$i ||