Gas coins should not be double-checked if GenericSignature is of type MoveAuthenticator. This happens in iota-core/authority when check_move_authenticator_input() is firstly invoked and, after validation, check_transaction_input() or check_certificate_input() are invoked.

Modify check_transaction_input(), check_transaction_input_with_given_gas(), check_certificate_input() in iota-transaction-checks to support a bool flag to pass down to check_gas(). This would allow to execute the checking only when the flag is true.