t / t4101 / diff.0-3on commit builtin-mktree.c: use a helper function to handle one line of input (fe0bb5f)
   1--- a/frotz
   2+++ b/frotz
   3@@ -1,2 +1,3 @@
   4 a
   5-b
   6+c
   7+b
   8\ No newline at end of file