Fix various issues found by profiling.

This commit is the result of inspecting the results of both cpu and
memory profiling, to improve areas where wallet can be more efficient
on transaction inserts.

One problem that's very evident by profiling is how much waiting there
is for file (txstore, wallet) writes.  This commit does not attempt to
fix this yet, but focuses on the easier-to-fix memory allocation
issues which can slow down the rest of wallet due to excessive garbage
collection scanning.

While here, fix a race where a closure run as a goroutine was closing
over a range iterator.

rpcserver.go

@@ -1369,7 +1369,7 @@ func (s *rpcServer) NotifyNewBlockChainHeight(bs *wallet.BlockStamp) {
 // TODO(jrick): Switch this to return a single JSON object
 // (map[string]interface{}) of all accounts and their balances, instead of
 // separate notifications for each account.
-func (s *rpcServer) NotifyBalances(wsc *websocketClient) {
+func (s *rpcServer) NotifyBalances() {
 	for _, a := range AcctMgr.AllAccounts() {
 		balance := a.CalculateBalance(1)
 		unconfirmed := a.CalculateBalance(0) - balance
@@ -2687,49 +2687,3 @@ func (s *rpcServer) NotifyNewTxDetails(account string, details btcjson.ListTrans
 	}
 	s.broadcasts <- mntfn
 }
-
-// NotifiedRecvTxRequest is used to check whether the outpoint of
-// a received transaction has already been notified due to
-// arriving first in the btcd mempool.
-type NotifiedRecvTxRequest struct {
-	op       btcwire.OutPoint
-	response chan NotifiedRecvTxResponse
-}
-
-// NotifiedRecvTxResponse is the response of a NotifiedRecvTxRequest
-// request.
-type NotifiedRecvTxResponse bool
-
-// NotifiedRecvTxChans holds the channels to manage
-// StoreNotifiedMempoolTxs.
-var NotifiedRecvTxChans = struct {
-	add, remove chan btcwire.OutPoint
-	access      chan NotifiedRecvTxRequest
-}{
-	add:    make(chan btcwire.OutPoint),
-	remove: make(chan btcwire.OutPoint),
-	access: make(chan NotifiedRecvTxRequest),
-}
-
-// StoreNotifiedMempoolRecvTxs maintains a set of previously-sent
-// received transaction notifications originating from the btcd
-// mempool. This is used to prevent duplicate client transaction
-// notifications once a mempool tx is mined into a block.
-func StoreNotifiedMempoolRecvTxs(add, remove chan btcwire.OutPoint,
-	access chan NotifiedRecvTxRequest) {
-
-	m := make(map[btcwire.OutPoint]struct{})
-	for {
-		select {
-		case op := <-add:
-			m[op] = struct{}{}
-
-		case op := <-remove:
-			delete(m, op)
-
-		case req := <-access:
-			_, ok := m[req.op]
-			req.response <- NotifiedRecvTxResponse(ok)
-		}
-	}
-}