pull: prevent duplicated entry in `op.pulledsubset`

In the bare pull case we could add the same node multiple time to the
`pulloperation.pulledsubset`. Beside being a bit wrong this confused the new
revset implementation of `revset._revancestor` into giving bad result.

This changeset fix the pull operation part. The fix for the revset itself will
come in another changeset.

mercurial/exchange.py

@@ -409,7 +409,12 b' class pulloperation(object):'
         if self.heads is None:
             # We pulled every thing possible
             # sync on everything common
-            return self.common + self.rheads
+            c = set(self.common)
+            ret = list(self.common)
+            for n in self.rheads:
+                if n not in c:
+                    ret.append(n)
+            return ret
         else:
             # We pulled a specific subset
             # sync on this subset