Adding patch by Jeffrey Harris optimizing rrule.__contains__().
diff --git a/dateutil/rrule.py b/dateutil/rrule.py
index b9f8f94..e229387 100644
--- a/dateutil/rrule.py
+++ b/dateutil/rrule.py
@@ -153,6 +153,8 @@
             for i in self:
                 if i == item:
                     return True
+                elif i > item:
+                    return False
         return False
 
     # __len__() introduces a large performance penality.