Subtract fee from amount

Fixes #2724 and #1570.

Adds the
automatically-subtract-the-fee-from-the-amount-and-send-whats-left
feature to the GUI and RPC (sendtoaddress,sendmany).

src/qt/walletmodeltransaction.cpp

@@ -46,6 +46,38 @@ void WalletModelTransaction::setTransactionFee(const CAmount& newFee)
     fee = newFee;
 }
 
+void WalletModelTransaction::reassignAmounts(int nChangePosRet)
+{
+    int i = 0;
+    for (QList<SendCoinsRecipient>::iterator it = recipients.begin(); it != recipients.end(); ++it)
+    {
+        SendCoinsRecipient& rcp = (*it);
+
+        if (rcp.paymentRequest.IsInitialized())
+        {
+            CAmount subtotal = 0;
+            const payments::PaymentDetails& details = rcp.paymentRequest.getDetails();
+            for (int j = 0; j < details.outputs_size(); j++)
+            {
+                const payments::Output& out = details.outputs(j);
+                if (out.amount() <= 0) continue;
+                if (i == nChangePosRet)
+                    i++;
+                subtotal += walletTransaction->vout[i].nValue;
+                i++;
+            }
+            rcp.amount = subtotal;
+        }
+        else // normal recipient (no payment request)
+        {
+            if (i == nChangePosRet)
+                i++;
+            rcp.amount = walletTransaction->vout[i].nValue;
+            i++;
+        }
+    }
+}
+
 CAmount WalletModelTransaction::getTotalTransactionAmount()
 {
     CAmount totalTransactionAmount = 0;