Progress #5: Hash IDs for generated transactions

As discussed on #5, use hashes as the generated_transaction_id_type
instead of serial numbers.

libraries/app/application.cpp

@@ -539,6 +539,8 @@ namespace detail {
                for (const auto& cycle : blk_msg.block.cycles)
                   for (const auto& thread : cycle)
                      for (const auto& transaction : thread.input_transactions)
+                        // In theory, we can ignore generated transactions here, since they don't ever go bare over the
+                        // network. Is this true?...
                         if (transaction.which() == decay_t<decltype(transaction)>::tag<signed_transaction>::value) {
                            eos::net::trx_message transaction_message(transaction.get<signed_transaction>());
                            contained_transaction_message_ids.push_back(eos::net::message(transaction_message).id());

libraries/chain/include/eos/chain/protocol/types.hpp

@@ -123,13 +123,12 @@ namespace eos { namespace chain {
    using account_id_type = chainbase::oid<account_object>;
    using producer_id_type = chainbase::oid<producer_object>;
 
-   using generated_transaction_id_type = uint32_t;
    using block_id_type = fc::ripemd160;
    using checksum_type = fc::ripemd160;
    using transaction_id_type = fc::ripemd160;
    using digest_type = fc::sha256;
+   using generated_transaction_id_type = fc::sha256;
    using signature_type = fc::ecc::compact_signature;
-   using share_type = safe<int64_t>;
    using weight_type = uint16_t;
 
    struct public_key_type

libraries/chain/protocol/block.cpp

@@ -91,9 +91,16 @@ namespace eos { namespace chain {
       vector<digest_type> ids;
       std::transform(input_transactions.begin(), input_transactions.end(), std::back_inserter(ids),
                      [](const input_transaction& trx) {
-         if (trx.which() == input_transaction::tag<signed_transaction>::value)
-            return trx.get<signed_transaction>().merkle_digest();
-#warning How do I get the digest from a generated_transaction_id_type?...
+         struct {
+            using result_type = digest_type;
+            result_type operator() (const signed_transaction& t) {
+               return t.merkle_digest();
+            }
+            result_type operator() (const generated_transaction_id_type& id) {
+               return id;
+            }
+         } digester;
+         return trx.visit(digester);
       });
       std::transform(output_transactions.begin(), output_transactions.end(), std::back_inserter(ids),
                      std::bind(&generated_transaction::merkle_digest, std::placeholders::_1));