branch: deprecate --set-upstream and show help if we detect possible mistaken use

diff --git a/RelNotes b/RelNotes
index a479abbc60611a95d75a33b092a322cb5fa2832c..19bb2ebbe687d9ded1a5c82d28d4410de1e2f19f 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.7.2.1.txt
\ No newline at end of file
+Documentation/RelNotes/1.7.12.txt
\ No newline at end of file