Fix transactions.py py3 incompatibility

Author: karlfloersch

ethereum/transactions.py

@@ -155,6 +155,9 @@ def creates(self):
     def __eq__(self, other):
         return isinstance(other, self.__class__) and self.hash == other.hash
 
+    def __lt__(self, other):
+        return isinstance(other, self.__class__) and self.hash < other.hash
+
     def __hash__(self):
         return utils.big_endian_to_int(self.hash)