diffcore-rename: fall back to -C when -C -C busts the rename limit

diff --git a/RelNotes b/RelNotes
index 5217e8e5543a696660e3f275d9717e0656d786f8..540b756d2f64d8c8ebf927a707b9b2cc0a4c6151 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.7.2.3.txt
\ No newline at end of file
+Documentation/RelNotes/1.7.5.txt
\ No newline at end of file