message: Add more descriptive exception
diff: @@ -282,10 +282,8 @@ class producer_plugin_impl : public std::enable_shared_from_this<producer_plugin
  auto id = trx->id();
  if( chain.db().find<transaction_object, by_trx_id>(id) ) {
  auto r = std::make_shared<transaction_trace>();
  - r->except = fc::exception();
  + r->except = tx_duplicate( FC_LOG_MESSAGE(error, "duplicate transaction ${id}", ("id", id)) );
  return r;
  - // EOS_ASSERT( false, tx_duplicate,
  - // "duplicate transaction ${id}", ("id", id ) );
  }
  return publish_results_of(trx, _transaction_ack_channel, [&]() -> transaction_trace_ptr {
  