[c++11] Use std::unique_ptr for block creation.

CreateNewBlock returns a pointer for which the caller takes ownership.
Use std::unique_ptr to make this explicit and simplify handling of these
objects in getblocktemplate.

src/miner.cpp

@@ -29,6 +29,7 @@
 #include <boost/thread.hpp>
 #include <boost/tuple/tuple.hpp>
 #include <queue>
+#include <utility>
 
 using namespace std;
 
@@ -102,14 +103,14 @@ void BlockAssembler::resetBlock()
     blockFinished = false;
 }
 
-CBlockTemplate* BlockAssembler::CreateNewBlock(const CScript& scriptPubKeyIn)
+std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock(const CScript& scriptPubKeyIn)
 {
     resetBlock();
 
     pblocktemplate.reset(new CBlockTemplate());
 
     if(!pblocktemplate.get())
-        return NULL;
+        return nullptr;
     pblock = &pblocktemplate->block; // pointer for convenience
 
     // Add dummy coinbase tx as first transaction
@@ -164,7 +165,7 @@ CBlockTemplate* BlockAssembler::CreateNewBlock(const CScript& scriptPubKeyIn)
         throw std::runtime_error(strprintf("%s: TestBlockValidity failed: %s", __func__, FormatStateMessage(state)));
     }
 
-    return pblocktemplate.release();
+    return std::move(pblocktemplate);
 }
 
 bool BlockAssembler::isStillDependent(CTxMemPool::txiter iter)