t / t4101 / diff.2-0on commit setup: set env $GIT_WORK_TREE when work tree is set, like $GIT_DIR (d95138e)
   1--- a/frotz
   2+++ b/frotz
   3@@ -1,2 +1,2 @@
   4 a
   5-b
   6\ No newline at end of file
   7+b