message: respect `AccountName` s mentioned as the `code` member of a `Message` when scheduling
diff: #include <eos/chain/transaction.hpp>
  #include <random>
  +#include <set>
  namespace eos { namespace chain {
  using pending_transaction = static_variant<SignedTransaction const *, GeneratedTransaction const *>;
  @@ -111,10 +112,15 @@ namespace eos { namespace chain {
  }
  };
  - struct scope_extracting_visitor : public fc::visitor<vector<AccountName> const &> {
  + struct scope_extracting_visitor : public fc::visitor<std::set<AccountName>> {
  template <typename T>
  - vector<AccountName> const & operator()(const T &trx_p) const {
  - return trx_p->scope;
  + std::set<AccountName> operator()(const T &trx_p) const {
  + std::set<AccountName> unique_names(trx_p->scope.begin(), trx_p->scope.end());
  + for (auto const &m : trx_p->messages) {
  + unique_names.insert(m.code);
  + }
  +
  + return unique_names;
  }
  };
  