t / t4135 / diff-with spaces.diffon commit sha1_file: convert check_sha1_signature to struct object_id (17e6545)
   1--- post image.txt.orig 2010-08-18 20:13:31.544002255 -0500
   2+++ post image.txt      2010-08-18 20:13:31.544002255 -0500
   3@@ -1 +1 @@
   4-preimage
   5+postimage