localrepo: support 'rev in repo' syntax

mercurial/localrepo.py

@@ -128,6 +128,12 b' class localrepository(repo.repository):'
             return context.workingctx(self)
         return context.changectx(self, changeid)
 
+    def __contains__(self, changeid):
+        try:
+            return bool(self.lookup(changeid))
+        except error.RepoLookupError:
+            return False
+
     def __nonzero__(self):
         return True