message: Modified transaction expiration to use the program options callback
  instead of hardcoded value.
diff: @@ -959,7 +959,6 @@ int main( int argc, char** argv ) {
  bool loop = false;
  benchmark_transfer->add_option("accounts", number_of_accounts, localized("the number of accounts in transfer among"))->required();
  benchmark_transfer->add_option("count", number_of_transfers, localized("the number of transfers to execute"))->required();
  - benchmark_transfer->add_option("expiration", expiration, localized("the number of seconds to expire"))->required();
  benchmark_transfer->add_option("loop", loop, localized("whether or not to loop for ever"));
  add_standard_transaction_options(benchmark_transfer);
  benchmark_transfer->set_callback([&]{
  @@ -1018,7 +1017,7 @@ int main( int argc, char** argv ) {
  vector<types::account_permission>{{sender,"active"}},
  "transfer", types::transfer{sender, recipient, amount, memo});
  - trx.expiration = info.head_block_time + fc::seconds(1800);
  + trx.expiration = info.head_block_time + tx_expiration;
  transaction_set_reference_block(trx, info.head_block_id);
  sign_transaction(trx);
  