Vanshdeep Singh f13c9a9d57 Problem: Stateful validation doesn't raise double spend exception (#2422)
* Problem: Stateful validation doesn't raise double spend exception

Solution: Transaction.validate should raise exception DoubleSpend if the given
transaction is already a part of the database

* Problem: Double spend exception message not accurate

Solution: The exception message should state that the double spend is because of
spending the same input more than once in the transaction
2018-07-31 14:06:21 +02:00
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