t / t4135 / diff-with tab.diffon commit helper/test-ref-store: fix "new-sha1" vs "old-sha1" typo (3c27e2e)
   1--- post        image.txt.orig  2010-08-18 20:13:31.616002255 -0500
   2+++ post        image.txt       2010-08-18 20:13:31.616002255 -0500
   3@@ -1 +1 @@
   4-preimage
   5+postimage