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

diff --git a/RelNotes b/RelNotes
index 17d37af54951e3179282cad837ee0beb271eb4e9..155555ef6af91ee7309a047f8280c1c57cac1e62 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.7.2.5.txt
\ No newline at end of file
+Documentation/RelNotes/1.8.2.3.txt
\ No newline at end of file