wallet: new transaction construction algorithm

It should avoid a lot of the issues sending more than half the
wallet's contents due to change.

Actual output selection is still random. Changing this would
improve the matching of transaction amounts to output sizes,
but may have non obvious effects on blockchain analysis.

Mapped to the new transfer_new command in simplewallet, and
transfer uses the existing algorithm.

To use in RPC, add "new_algorithm: true" in the transfer_split
JSON command. It is not used in the transfer command.

src/simplewallet/simplewallet.cpp

@@ -353,6 +353,7 @@ simple_wallet::simple_wallet()
   m_cmd_binder.set_handler("payments", boost::bind(&simple_wallet::show_payments, this, _1), tr("payments <payment_id_1> [<payment_id_2> ... <payment_id_N>] - Show payments <payment_id_1>, ... <payment_id_N>"));
   m_cmd_binder.set_handler("bc_height", boost::bind(&simple_wallet::show_blockchain_height, this, _1), tr("Show blockchain height"));
   m_cmd_binder.set_handler("transfer", boost::bind(&simple_wallet::transfer, this, _1), tr("transfer [<mixin_count>] <addr_1> <amount_1> [<addr_2> <amount_2> ... <addr_N> <amount_N>] [payment_id] - Transfer <amount_1>,... <amount_N> to <address_1>,... <address_N>, respectively. <mixin_count> is the number of transactions yours is indistinguishable from (from 0 to maximum available)"));
+  m_cmd_binder.set_handler("transfer_new", boost::bind(&simple_wallet::transfer_new, this, _1), tr("Same as transfer, but using a new transaction building algorithm"));
   m_cmd_binder.set_handler("sweep_dust", boost::bind(&simple_wallet::sweep_dust, this, _1), tr("Send all dust outputs to the same address with mixin 0"));
   m_cmd_binder.set_handler("set_log", boost::bind(&simple_wallet::set_log, this, _1), tr("set_log <level> - Change current log detalization level, <level> is a number 0-4"));
   m_cmd_binder.set_handler("address", boost::bind(&simple_wallet::print_address, this, _1), tr("Show current wallet public address"));
@@ -1254,7 +1255,7 @@ bool simple_wallet::show_blockchain_height(const std::vector<std::string>& args)
 }
 
 //----------------------------------------------------------------------------------------------------
-bool simple_wallet::transfer(const std::vector<std::string> &args_)
+bool simple_wallet::transfer_main(bool new_algorithm, const std::vector<std::string> &args_)
 {
   if (!try_connect_to_daemon())
     return true;
@@ -1410,7 +1411,11 @@ bool simple_wallet::transfer(const std::vector<std::string> &args_)
   try
   {
     // figure out what tx will be necessary
-    auto ptx_vector = m_wallet->create_transactions(dsts, fake_outs_count, 0 /* unlock_time */, 0 /* unused fee arg*/, extra);
+    std::vector<tools::wallet2::pending_tx> ptx_vector;
+    if (new_algorithm)
+      ptx_vector = m_wallet->create_transactions_2(dsts, fake_outs_count, 0 /* unlock_time */, 0 /* unused fee arg*/, extra);
+    else
+      ptx_vector = m_wallet->create_transactions(dsts, fake_outs_count, 0 /* unlock_time */, 0 /* unused fee arg*/, extra);
 
     // if more than one tx necessary, prompt user to confirm
     if (m_wallet->always_confirm_transfers() || ptx_vector.size() > 1)
@@ -1523,6 +1528,16 @@ bool simple_wallet::transfer(const std::vector<std::string> &args_)
 
   return true;
 }
+//----------------------------------------------------------------------------------------------------
+bool simple_wallet::transfer(const std::vector<std::string> &args_)
+{
+  return transfer_main(false, args_);
+}
+//----------------------------------------------------------------------------------------------------
+bool simple_wallet::transfer_new(const std::vector<std::string> &args_)
+{
+  return transfer_main(true, args_);
+}
 
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::sweep_dust(const std::vector<std::string> &args_)

src/simplewallet/simplewallet.h

@@ -108,7 +108,9 @@ namespace cryptonote
     bool show_incoming_transfers(const std::vector<std::string> &args);
     bool show_payments(const std::vector<std::string> &args);
     bool show_blockchain_height(const std::vector<std::string> &args);
+    bool transfer_main(bool new_algorithm, const std::vector<std::string> &args);
     bool transfer(const std::vector<std::string> &args);
+    bool transfer_new(const std::vector<std::string> &args);
     bool sweep_dust(const std::vector<std::string> &args);
     std::vector<std::vector<cryptonote::tx_destination_entry>> split_amounts(
         std::vector<cryptonote::tx_destination_entry> dsts, size_t num_splits