t / t4101 / diff.1-3on commit t/t7800-difftool.sh: Skip with prereq on no PERL (2c4f302)
   1--- a/frotz
   2+++ b/frotz
   3@@ -1,3 +1,3 @@
   4 a
   5-b
   6 c
   7+b
   8\ No newline at end of file