Merge with stable.

Merge with stable.

--- a/mercurial/obsolete.py	Fri Nov 08 12:45:52 2013 +0900
+++ b/mercurial/obsolete.py	Sun Nov 17 13:42:24 2013 -0500
@@ -267,7 +267,8 @@
         Return the number of new marker."""
         if not _enabled:
             raise util.Abort('obsolete feature is not enabled on this repo')
-        new = [m for m in markers if m not in self._all]
+        known = set(self._all)
+        new = [m for m in markers if m not in known]
         if new:
             f = self.sopener('obsstore', 'ab')
             try: