t9300: use perl "head -c" clone in place of "dd bs=1 count=16000" kluge

diff --git a/RelNotes b/RelNotes
index 8abe4c292b53249d22252f54c877a798ff604327..b942e499449d97aeb50c73ca2bdc1c6e6d528743 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.5.1.5.txt
\ No newline at end of file
+Documentation/RelNotes/1.7.4.txt
\ No newline at end of file