py3: make 'None in lazyancestors' not crash

This looks somewhat weird, but we have callers like 'torev(n) in futurecommon'
around where torev(n) is dictlike.get(n). I could fix callers, but that would
be unnecessarily verbose.

mercurial/ancestor.py

@@ -339,6 +339,10 b' class lazyancestors(object):'
         seen = self._containsseen
         if target in seen:
             return True
+        # Only integer target is valid, but some callers expect 'None in self'
+        # to be False. So we explicitly allow it.
+        if target is None:
+            return False
 
         parentrevs = self._parentrevs
         visit = self._containsvisit