revert: bring back usage of `subset & ps` in `parents` Changeset 95af98616aa7 switched the order of the operand of the "&" computation to work around an issue from repo-wide spanset. The need for a workaround has been alleviated by the introduction of `fullreposet`. So we restore it to normal. The benchmark shows no significant changes as expected. We also revert the bogus test change introduced by 95af98616aa7. The order is actually important.

--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1242,7 +1242,7 @@
         for r in getset(repo, spanset(repo), x):
             ps.update(cl.parentrevs(r))
     ps -= set([node.nullrev])
-    return baseset(ps) & subset
+    return subset & ps
 
 def parentspec(repo, subset, x, n):
     """``set^0``