t / t4135 / diff-with backslash.diffon commit diff.c: pass sign_index to emit_line_ws_markup (bc9feb0)
   1--- post\image.txt.orig 2010-08-18 20:13:31.680002255 -0500
   2+++ post\image.txt      2010-08-18 20:13:31.680002255 -0500
   3@@ -1 +1 @@
   4-preimage
   5+postimage