gc: reject if another gc is running, unless --force is given

diff --git a/RelNotes b/RelNotes
index 540b756d2f64d8c8ebf927a707b9b2cc0a4c6151..155555ef6af91ee7309a047f8280c1c57cac1e62 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.7.5.txt
\ No newline at end of file
+Documentation/RelNotes/1.8.2.3.txt
\ No newline at end of file