clfilter: fix a false positive in the test-obsolete.t

We push between two repo which once filtered looks unrelated. Weakness in the
current implementation allows this push to be done without -f. But later
improvement with filtering will make this push fails for unrelatedness. However
we want this push to fail for including bumped changeset. So we had a smaller
push --force to make them related.

tests/test-obsolete.t

@@ -173,6 +173,13 b' the public changeset'
 
 And that we can't push bumped changeset
 
+  $ hg push ../tmpa -r 0 --force #(make repo)
+  pushing to ../tmpa
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 1 changes to 1 files (+1 heads)
   $ hg push ../tmpa
   pushing to ../tmpa
   searching for changes