Batch block connection during IBD

During the initial block download (or -loadblock), delay connection
of new blocks a bit, and perform them in a single action. This reduces
the load on the database engine, as subsequent blocks often update an
earlier block's transaction already.

src/wallet.h

@@ -659,11 +659,7 @@ public:
     int GetRequestCount() const;
 
     void AddSupportingTransactions();
-
-    bool AcceptWalletTransaction(CCoinsDB& coinsdb, bool fCheckInputs=true);
-    bool AcceptWalletTransaction();
-
-    void RelayWalletTransaction(CCoinsDB& coinsdb);
+    bool AcceptWalletTransaction(bool fCheckInputs=true);
     void RelayWalletTransaction();
 };