Respect --changeaccount with unmixed ticket autobuying

There is currently no way to set the change account used by individual split
transactions when running the ticket autobuyer without mixing, as this account
was never looked up from the config.  Allow the change account to be specified
with unmixed ticket buying, defaulting to the purchase account if it is unset.
The change account remains required if mixing is enabled.

Author: jrick

config.go

@@ -174,7 +174,7 @@ type config struct {
 	mixedAccount       string
 	mixedBranch        uint32
 	TicketSplitAccount string `long:"ticketsplitaccount" description:"Account to derive fresh addresses from for mixed ticket splits; uses mixedaccount if unset"`
-	ChangeAccount      string `long:"changeaccount" description:"Account used to derive unmixed CoinJoin outputs in CoinShuffle++ protocol"`
+	ChangeAccount      string `long:"changeaccount" description:"Account to send change when ticket autobuying or mixing; required when mixing"`
 	MixChange          bool   `long:"mixchange" description:"Use CoinShuffle++ to mix change account outputs into mix account"`
 	MixSplitLimit      int    `long:"mixsplitlimit" description:"Maximum concurrent mixes for any change amount"`
 

dcrwallet.go

@@ -301,7 +301,7 @@ func run(ctx context.Context) error {
 				purchaseAccount    uint32 // enableticketbuyer
 				votingAccount      uint32 // enableticketbuyer
 				mixedAccount       uint32 // (enableticketbuyer && mixing) || mixchange
-				changeAccount      uint32 // (enableticketbuyer && mixing) || mixchange
+				changeAccount      uint32 // enableticketbuyer || mixchange
 				ticketSplitAccount uint32 // enableticketbuyer && mixing
 			)
 			if cfg.EnableTicketBuyer {
@@ -317,6 +317,11 @@ func run(ctx context.Context) error {
 				} else {
 					votingAccount = purchaseAccount
 				}
+				if cfg.ChangeAccount != "" {
+					changeAccount = lookup("changeaccount", cfg.ChangeAccount)
+				} else {
+					changeAccount = purchaseAccount
+				}
 			}
 			if (cfg.EnableTicketBuyer && cfg.MixingEnabled) || cfg.MixChange {
 				mixedAccount = lookup("mixedaccount", cfg.mixedAccount)