[PATCH] scmutil: seen.union should be seen.update (issue3476)

[Bryan O'Sullivan]

# HG changeset patch
# User Bryan O'Sullivan <bryano at fb.com>
# Date 1338522930 25200
# Node ID 748222250cca41a3f97663a83ee312e958ffd4c0
# Parent  34f4e2af3cad277b16dcf44a75fbf8ddfa0e76d8
scmutil: seen.union should be seen.update (issue3476)

diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -569,7 +569,7 @@ def revrange(repo, revs):
                 newrevs = set(xrange(start, end + step, step))
                 if seen:
                     newrevs.difference_update(seen)
-                    seen.union(newrevs)
+                    seen.update(newrevs)
                 else:
                     seen = newrevs
                 l.extend(sorted(newrevs, reverse=start > end))