scmutil: speed up new-style range extension

This improves perfrevset performance by 10% for 2222::33333 on a
kernel repo.

mercurial/scmutil.py

@@ -584,10 +584,9 b' def revrange(repo, revs):'
 
         # fall through to new-style queries if old-style fails
         m = revset.match(repo.ui, spec)
-        for r in m(repo, range(len(repo))):
-            if r not in seen:
-                l.append(r)
-        seen.update(l)
+        dl = [r for r in m(repo, xrange(len(repo))) if r not in seen]
+        l.extend(dl)
+        seen.update(dl)
 
     return l