add expire-dumps

Signed-off-by: Joerg Jaspert <joerg@debian.org>

diff --git a/scripts/backports/expire_dumps b/scripts/backports/expire_dumps
new file mode 120000 (symlink)
index 0000000..02095f6
--- /dev/null
+++ b/scripts/backports/expire_dumps
@@ -0,0 +1 @@
+/develop/vcs/dak/dak/scripts/debian/expire_dumps
\ No newline at end of file