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/init.cpp

@@ -50,6 +50,8 @@ void StartShutdown()
 #endif
 }
 
+static CCoinsViewDB *pcoinsdbview;
+
 void Shutdown(void* parg)
 {
     static CCriticalSection cs_Shutdown;
@@ -74,6 +76,12 @@ void Shutdown(void* parg)
         nTransactionsUpdated++;
         bitdb.Flush(false);
         StopNode();
+        {
+            LOCK(cs_main);
+            pcoinsTip->Flush();
+            delete pcoinsTip;
+            delete pcoinsdbview;
+        }
         bitdb.Flush(true);
         boost::filesystem::remove(GetPidFile());
         UnregisterWallet(pwalletMain);
@@ -298,6 +306,7 @@ std::string HelpMessage()
     return strUsage;
 }
 
+
 /** Initialize bitcoin.
  *  @pre Parameters should be parsed and config file should be read.
  */
@@ -641,6 +650,9 @@ bool AppInit2()
     uiInterface.InitMessage(_("Loading block index..."));
     printf("Loading block index...\n");
     nStart = GetTimeMillis();
+    pcoinsdbview = new CCoinsViewDB();
+    pcoinsTip = new CCoinsViewCache(*pcoinsdbview);
+
     if (!LoadBlockIndex())
         return InitError(_("Error loading blkindex.dat"));