get_ref_dir(): take the containing directory as argument

diff --git a/RelNotes b/RelNotes
index 766bbaf8f5a90759645200e1fc61e11d9836de49..bcb4fb98ff925389797125283e40c6e397efc1fd 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.7.9.txt
\ No newline at end of file
+Documentation/RelNotes/1.7.11.txt
\ No newline at end of file