use CBlockIndex* insted of uint256 for UpdatedBlockTip signal

- removes mapBlockIndex find operation
- theoretically allows removing the cs_main lock during zqm notification while introducing a new file position lock

src/zmq/zmqabstractnotifier.h

@@ -7,7 +7,9 @@
 
 #include "zmqconfig.h"
 
+class CBlockIndex;
 class CZMQAbstractNotifier;
+
 typedef CZMQAbstractNotifier* (*CZMQNotifierFactory)();
 
 class CZMQAbstractNotifier
@@ -30,7 +32,7 @@ public:
     virtual bool Initialize(void *pcontext) = 0;
     virtual void Shutdown() = 0;
 
-    virtual bool NotifyBlock(const uint256 &hash);
+    virtual bool NotifyBlock(const CBlockIndex *pindex);
     virtual bool NotifyTransaction(const CTransaction &transaction);
 
 protected: